87 year old MIL wants to move in but....

My mother in law is 87 years old and physically healthy. Not sure if it is the mental illness or her culture but she does not believe in western medicine. She has been verbally abusive to my husband, her only son, for all his life. She has little friends because she has serious boundary issues and pushes people away. She believes that something is wrong with them and it is never her. Her relatives (sister, nieces & nephews) want nothing to do with her, well unless they need money. My husband's father, I suspect, realized how mentally ill this woman is and took off not long after he was born.

Lately she has been pestering my husband to move in. We have tried to live with her in the past but it was next to impossible with the snooping, meddling and stealing. She would at times take things of ours, like a hairbrush, and defiantly claim it as hers because she bought it (at least she thought so). She has been extremely toxic to our blended family while the kids were growing up. I have children from a prior marriage who she told our son aren't really his siblings and made fun of one of them who had a weight issue.

I am somewhat concerned about her mostly because of her age. She has alienated a lot of people. She claims to be depressed and says living with us will make her feel better but I know it wont. She has been manipulative in the past and I suspect this "depression" as further manipulation. She has done well for herself financially so it isn't like she needs help with that. I feel bad because she is older but I keep reminding myself that she will wreak havoc on our family if she comes to live with us. I dont know if there are any kind of resources out there for her like case management? The thing is she believes she is fine but that there is something wrong with everybody else.

Thanks in advance for any feedback!