Can anyone tell me if they ever did an appeal through Medicare?

If this is about placement to a SNF for rehab as a post hospitalization care, I think it would be very very difficult to “win” an appeal.
For rehab, they are doing exercises or activities every day, even multiple times a day. If they flat will not do or even make an effort to do stuff, all this will be detailed in their health chart. They are viewed as being at a “plateau” and discharged from rehab. It will be hard for you to disprove the “plateau”.

if elder is all uncooperative, their toast on staying in rehab imo. Do whatever you can to motivate them to participate. Yeah it’s hard, my mil was all “not gonna” after her hip replacement and off of rehab in under the 21 days usually done. Nothing motivated her, she wanted to stay in bed & be waited on & planning on returning to her past life.