Well, it sounds like this doctor doesn’t understand dementia, that’s for sure! Does he or she have any suggestions or make any comments about this?
I would say: bring the entertainment to her. Find out WHY she’s getting up. Does she think she has chores? Does she want to go watch TV or visit with people? Maybe bring her something to do in bed, like a task. Bring her stuff to fold (clothes, socks) or even dishes and silverware to sort. She’ll feel productive but she will still be sitting or laying down.
She can probably do these things with minimal arm movement. I would also suggest putting that arm in a sling.
Inevitably, she’s going to get up. We just want to minimize the amount of times she does that.