Do they have a gel mattress or an alternating air mattress on her bed?
What are the doctor's orders on how to treat the bedsores?
Have you talked to the doctor-or better yet put your observations and questions in writing? It's a sad fact, that most of the time when an older relative is in a rehab center, or extended care facility, someone responsible needs to become their advocate. And it is a hard job. Koala is right-putting things in writing will usually smooth out problems much quicker than talking.
I wish you luck.