Your husband is an enabler. YES, I realize that your future MIL has a mental illness, but at the same time, what right does she have to impose on everyone else? No, she's not responsible for having the problem, but she IS responsible for her own healing and its not right for her to put her baggage on everyone else. Sometimes people literally need to hit rock bottom before they get help. If she can't pay rent on the house your husband bought for her then maybe its time to sell the house. I know a lot of people will say that's cruel, but enabling doesn't do anything to help anyone heal. This woman needs tough love. I know you don't want to go the ultimatum route, but just look at what your future will be. Enabling this woman is just going to get her in deeper. You can present "tools" for healing to her, but if she refuses them then its completely on her.