18 years ago we sold our home and moved in with dh's MIL, yes my (d)m. I am an only child. It was a 3-storey 6 bedroom house and the agreement was to share kitchen, morning room and bathroom, with us having a bedroom and sitting room on the top floor. We were to pay all the maintenance and bills. I had just started re-training in a new career and she was in her 70s. We knew the stress of worrying about house and garden, both maintenance and bills would be debilitating so thought it would be easier in the long run.....
We were wrong. Within 6 weeks, whilst still content for us to pay all the bills, and to filch expensive bottles of wine from us, she had to all intent stopped speaking to us. Further on, it became 'inconvenient' for us to use the washing machine at weekends ffs. So, happy to comply, we used to go to the launderette and have a toastie next door while waiting.
6 months later, we moved out, without a forwarding address and a new ex-directory phone no, the week after she wrote me a letter telling me she didn't consider me her daughter. She even managed to get our new address from a temp postie over Christmas, and when complained told the post office that 'her daughter' gave her our address = did I heck as like!
Then followed about 3-4 years of anonymous letters from her, and others from people she knew offering to bring her over for afternoon tea as she was so upset I wasn't speaking to her [hmmm]. She is one of those narcissistic bullies that when things don't go her way, stops speaking and creates a sub-zero atmosphere so that everyone rushes round trying to cajole her - bit like a bad-tempered siamese IYSWIM, with apologies to siamese cat lovers.
Hardly surprising I failed my first exams, then was made redundant when passing them 6 months later. Still, I got out. 
The moral of this story is tread very, very carefully. Don't, as I did, put down odd previous behaviour to an unhappy marriage, if a parent has always been odd, behaved unreasonably, etc, they always will, and once they have you where they want you, can only get worse.