how hard can you push?

My sister-in-law had a major stroke a couple of years ago and has marginal use of her left arm and leg. She has done the professional rehab with some results but not great. While Brother was working she was ok alone for the day if he checked on her over lunch break. She was doing some little things around the house to help out, otherwise he worked full time, did all her care and all the day to day stuff required to run a household. He recently retired from his job and is home full time. Needless to say, he is getting burned out. My frustration is her lack of seeing all that he does. She no longer even attempts to be of help around the house and refuses professional rehab, or even do the exercises she should be doing on her own. I am aware that her mind was effected by the stroke and the situation is not her fault. But she seems oblivious to how much this is costing him. My question is how, or if she can be convinced to contribute as much as she can to their daily living situation. He gets tired of nagging her, she gets tired of hearing it. His health is beginning to suffer. I'd love to find some advice that would truely help, just don't know where to find it. I am fond of her. She didn't ask for this situation but she does nothing to improve it. Can anyone pass on some advice?