While not an exact comparison, my MIL is going through something similar with her oldest daughter.
Jennie is 66 years old and has always been a large person. Probably 5'-8" and has always been well over 250 lbs. She came over to help us pack up in preparation for our move. This was August and we hadn't seen her since Christmas. She had lost 75 lbs without trying. Huge 
, but she was unconcerned. She also feel at least twice while she was at our house. Fast forward a month and Jennie took her mom and uncle on a 10 hour drive to visit another aunt. This aunt's daughter was there and she just happens to be a Dr. who ran a palliative care facility. So maybe she knows something. She told Jennie that from looking at her she suspected diabetes, but Jennie blew her off.
Went to visit over Thanksgiving and Jennie was using a walker to get around. By Christmas, she had stopped driving, moved into her mom's house and was basically unable to walk. She finally went to the Dr and guess what, she had diabetes and had basically lost function of her legs. So she was sent to rehab to try and build up her strength. She got there and proceeded to keep doing things that got her sent back to the hospital. Finally my MIL gave up and let her come home saying she wasn't going to send her off someplace to die. It was rehab, not a long-term care facility. So today she is bedridden and my 89 year old MIL is her carer. Jennie doesn't want anyone else doing thing so hiring outside help is out of the question. So she is doing her best to kill her mom, whom she has never gotten along with. My MIL is looking at this as a way to fix a relationship, but Jennie wants no part of that.
And in an almost identical situation, her mom goes to Starbucks on an almost daily basis to get her scones and some way over-sugared drink because that is all she will eat.
This is the reason our Living Wills have been updated to specifically say my MIL is to have zero say in our care if needed. She has shown she is unwilling to do what is necessary to provide proper care for Jennie, so she probably wouldn't for either of us. So she's out.
