Mother-in-law took a fall and ended up in ICU and just came home after 8 days. What can we expect for a plan to keep her healthy?

Pressure sores need wound care. Time for immediate assessment by the MD and ordering of wound care. She may be transferred to SNF. If these are decubiti you need to understand that they can quickly go to the bone, can quickly cause systemic sepsis and can be killer in short order with all organs shutting down.
This is, if there are serious sore here, a LIFE THREATENING condition.
It is time to ignore what MIL says and to get assessment and care.
Call the MD today. That an RN told you there are pressure sores and did nothing about discharge planning is ASTOUNDINGLY bad care.
Call the MD asap.

Why oh why was she not sent to post hospitalization rehabilitation?

rehab would have been in a NH with a rehab sector OR at a purely rehabilitation facility. Both wouod be a post hospitalization benefit covered under part A coverage of Medicare. The standard kinda is rehab is done 20/21 days as Medicare coverage is 100% for that precise time period ( assuming a patient is attempting to be compliant with care).

If she "just" came home, there is probably a window of opportunity to get her into in-patient rehab

Call the discharge planning unit at the hospital and correct this error.

Muscles will deteriorate if they are not used. Bedsores will develop when a person stays in one spot.

My mother had mobility issues due to Parkinson’s disease. She took her share of tumbles. Terrible injuries can happen when an elderly person falls.

Mom’s doctor ordered home health several times to build her strength and work on balancing issues.

The last time mom was in the hospital rehabilitation was ordered for her. Mom actually started doing some physical therapy exercises in the hospital before they transported her directly to the rehab facility.

My mother was in her 90’s and worked extremely hard in rehab. It truly helps for those who are capable of doing the work. It’s a tough work out but pays off in the end.

As far as the recliner goes, mom’s home health team suggested a pillow made to sit in her recliner with.

The occupational therapist also rearranged her bedroom furniture to suit her needs better. Mom needed the assistance of bedside rails to grab onto to get out of bed. You can purchase the pillow and rails on Amazon.

Our RN nurse from our home health services was also a wound care specialist. They know how to care for bedsores. Bedsores are difficult to manage if they have been there for a while.

Please try to set up rehab for your mom. It’s worth a try. Or at least home health care. Good luck in resolving this issue.

What was her injury? Head? Other? Was it due to a stroke?

Was she non-compliant in the hospital and that's why she was discharged? And her husband agreed to take her back? If so, he's the main problem.

If neither of them are making decisions in your MIL's best interests then her PoA (and hopefully she has one) now needs to step in.

As the other savvy retired RNs on this forum have said, MIL needs wound care and the hospital should not have discharged her without a plan. Or, maybe there was a plan and FIL didn't remember/care about it?

If she needs to go back to the hospital for any reason her PoA or other family member needs to tell the staff that she is an unsafe discharge. Her PoA needs to do what activates their authority to override FILs inadequate caregiving. It will be the best opportunity to have her go directly into rehab, or a facility. I wish you success in getting her the proper care!

Part 2 of 2

The second advice for you is that in a well-run and disciplined caregiving system, the person who is charged as the main caregiver must be at the helm. Others can make suggestions to her, but they should not interfere. If this primary requirement does not happen, then there will be chaos and the quality of life for the patient and the whole family will go down. Here is a cut and paste from my recent book "Dementia Care Companion":

Primary Caregiver at the Helm
The primary caregiver is the most critical element of a successful care program and the primary pillar on which everything else rests. The primary caregiver must not only do most of the heavy lifting in day-to-day care of the patient, but must also take on a leadership role, directing all aspects of the care program, including marshalling financial and human resources of the family to get the job done. 

Getting Everyone to Pull Together
Once dementia appears on the horizon, there is a short window of opportunity to address important questions about the future, progression of dementia, care plans, financial and legal affairs, and so on. Care issues will only grow more challenging over time, and it is important to get the care effort going in the right direction from the very beginning or as early as possible. 

In some cases, care planning is straightforward. If you are caring for your spouse, are physically and mentally healthy, have the necessary financial means, and enjoy the unconditional support of your children, then managing the care process is relatively straightforward. You can make all the decisions with the sole focus on what is best for the patient, without having to worry about approval or interference from others.
Often, however, things are not that simple. Even close family members do not always arrive at the same conclusion at the same time. They may disagree about the nature of the problem or how best to go about solving it. Sometimes, family members might put up obstacles, rather than participate constructively. When planning for care, it is important to address interpersonal issues early on and continue on an ongoing basis.
·        When planning your care strategy, have a meeting with all the stakeholders present. Discuss caregiving and related issues, including legal, financial, management, and follow-through of the plans over time. Try to reach consensus among all the parties.
·        Don’t assume that everyone is on the same page regarding care planning and decisions. Most likely, you’ll find that various members of the family have different ideas and disagree on the correct approach. Discuss the issues early on and try to reach an agreement so everyone is on the same page, supports the plan, and works toward its success.
·        Past grudges among family members may make it impossible for everyone to get along. Some members of the family may constantly create problems and find faults with others, without providing any help themselves. Sometimes, the best thing to do is to let them get it off their chest and then move on with the real work of planning.
·        If there are many disagreements and deep family grudges going back many years, especially among the primary family members, it may help to have a neutral body, such as the family attorney or a counselor, present during these meetings.

My first instinct was to question why she was not sent to rehab first before discharge home since there are fall and bedsore concerns. A good rehab facility would offer PT for balance issues, etc, and a wound care specialist for the developing bed sores. And, you would have time to make home arrangements. But, not all rehab facilities are created equal. Not all facilities have competent and attentive staff, so she may not have lost much by not going. However, make sure the hospitalist has ordered home health care which is covered by Medicare for a period of several days. She needs a wound care nurse to follow-up at the house and PT to work on balance and any other issues with mobility. PT will also evaluate the house for her needs and for safety. Take advantage of those services.
Now the big issues, (we will get back to bedsores):
1) Who is in charge of her care?
2) Who has medical and financial POA?
3) Is her house safe for her and accessible? Grab bars in bathroom/shower? Ramps and rubber threshold covers to get over porch stairs and over high thresholds? Handrail installed down long hallways? It can be used as both a safety feature and for exercise/therapy. Canes, walkers, shower chairs, wheelchairs available?
4) Does your FIL and MIL understand just how serious bedsores can be? Are they capable of making good decisions? If not, is there someone in the family they will listen to? - or a doctor?
I have lived the beginning bedsore scenario with my mother. It was actually caused by a rehab stay during COVID. The only thing that saved her is that once we got her home, we caught it early and took action. Movement and proper hygiene are your friends - the opposite will lead to real trouble - quickly.
Some people have recommended air mattresses that inflate in different places to basically move the person in bed. It might work for you. My mother did not like the feel of a “creeping” mattress so I had to abandon that. Next I tried a thick foam mattress topper made by Serta or Sealy (available at Kohl’s) that also helps keep her comfortably cool. I found that the mattress topper worked better and helped reduce the bedsore redness. The other thing is moving off her back to her side every two or three hours at the most during the day. At night I let it go - I need to sleep too!
It sounds like she could easily become bedridden if she continues to just stay in the chair with little movement - you probably don’t want that to happen. If she can regain the strength to safely continue to walk she needs to do it. Everything is harder care wise once they are bedridden- except I don’t have to worry about falls…

Lots of good advice given. I would focus on the pressure sore situation and while not trying to instill fear it is important to provide thorough information about them. They can go south very quickly. There are 5 stages the worse being unstageable which will still require treatment but it is very difficult for both the person doing it as well as the patient. Patient should be given serious pain medication at least half an hour before treatment which involves debriding dead tissue and using certain very specific medications. There may need to be twice daily packing of the wound. There may be a wound vac machine used. At worse stage it generally means that bone is visible and osteomyelitis may have set in which require serious antibiotics. Quite honestly it can be very difficult to recover from this ailment particularly in an already compromised individual. Perhaps calmly explaining this might make someone opt to stop sleeping in a lounge chair and choose the proper compression mattress at least as a starter.

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Part 1 of 2

I see two major problems with respect to your post. Let's deal with the more important one first, and that is pressure sore. Here is an excerpt from my recent book "Dementia Care Companion": 

Bedsores and Pressure Ulcers
If you apply pressure to a point on the skin, the pressure blocks blood flow through the capillaries at that point. If the pressure persists for a few hours, skin cells and the underlying tissue begin to die, creating a pressure ulcer. If the pressure continues still, the injury develops into an open sore, impacting muscle, bone, and other tissues at the affected area.
Pressure ulcers are often referred to as bedsores, since they usually develop as a result of prolonged confinement to bed. Conditions such as diabetes, infections, hospitalization, incontinence, inadequate or improper nutrition, and reduced awareness as a result of dementia are some of the other factors contributing to the development of pressure ulcers.

Who Is at Risk?
While sitting or sleeping, a healthy individual shifts around and changes position naturally to avoid prolonged pressure on any point on their body. A person with a medical condition that limits their ability to change positions cannot relieve pressure adequately, and is therefore at risk of developing bedsores. Elderly people, those with limited mobility due to injury or illness, and people who spend most of their time in bed or in a chair are at risk.

Prevention
Treating advanced bedsores is difficult and requires professional care. Advanced bedsores also take a long time to heal. Therefore, it is critical to prevent bedsores from developing in the first place. It takes vigilance to discover and treat bedsores right away, and to prevent them from advancing to more serious stages.

Daily Monitoring
·        Monitor vulnerable areas on the patient’s body in order to detect the first signs of potential trouble. Pay special attention to areas that are under pressure when sitting or lying down.
·        Every morning after waking the patient up, inspect the areas of their body susceptible to pressure during sleep. A good time for this is during morning stretches while the patient is still in bed.
·        Bathing time is an ideal opportunity to inspect the patient from head to toe for early signs of bedsores.
·        To inspect an area, press it gently with your finger. If the skin is healthy, its color will turn white under your finger, and will return back to its natural color when you remove the pressure.

Patient Handling
·        Do not leave the patient in one position for long periods.
·        When in bed, turn the patient every two hours so no part of their body is subjected to continuous pressure for more than two hours at a time.
·        Getting tangled up in bed sheets can put extra pressure on the skin. Prevent bed sheets from wrapping tightly around the patient’s limbs overnight.
·        Wet bedding creates more friction and increases the risk of skin damage. Change wet sheets and clothes right away.
·        When moving the patient, take care to not stretch or pull on their skin. It takes a moment of carelessness to scratch, break, or tear fragile skin. During patient transfers, for example from bed to wheelchair, take extra care of the skin at the hips and buttocks.

Health and Hygiene
·        The risks of developing advanced bedsores are higher if the patient is incontinent. A wound that comes into contact with urine or feces is in fertile grounds for infection.
·        Staying hydrated helps keep skin healthy and fresh and reduces the risk of bedsores. Do not wait until the patient is thirsty to give them fluids. They may be unable to communicate that they are thirsty, or may not even be aware of it.

Use Pressure-Relief Equipment
·        Invest in an alternating pressure mattress. These mattresses have air cells, such as tubes running later

Why did the ICU release your MIL to her home instead of sending her to rehab for therapies? I was in ICU when I had a brain aneurysm and after my ICU admission and recovery, I was sent to rehab for therapies. I was always under the impression that after an ICU admission the patient is then sent to rehab for therapies.