What is the problem with my MIL?

MIL had open heart surgery in August; she is 80...lifelong smoker with the beginning of COPD. After surgery, she was moved to rehab, it was determined that she'd had a small stroke either during or right after surgery. She has refused rehab, won't even do in bed PT, says she has no energy. She refuses to eat, says she wants to die. My BIL who is the health care proxy says that he wants to honor her wishes. (!!) She talks in a whisper, or mostly must mouths words; she will occasionally take a bite of food that someone brings in, makes faces when she tastes the RH center food. The social worker at the center says (at least according to BIL) that she's not depressed. Isn't wanting to die when you're not really ill with something terminal the definition of depression? What would any of you do faced with this situation. My husband is reluctant to intervene; the last time he tried to tell his mother that what she was doing was bad for her health she threatened to have him charged with Elder Abuse. Oy