A person with license to destroy

Okay, I've had several problems with my fiance's mother in the past. She let me move in with them rent-free for 2 years. In that 2 years, she always held that over my head to get whatever she wanted. She borrowed money from me for Bingo when I had a job there and never paid me back. That was a total of $80 or so that I'll never see again.
Afterwards, I got pregnant while on birth control. She accused me of trying to get pregnant while I didn't have a job. I had no money, no vehicle, nowhere else to turn. I had to stay there. She knew a month in advance for most of my doctors appointments, and unless Blaize's friends helped us get there, I missed them because she wanted to go to bingo instead. I signed up for Cash Assistance at this time so that I would be able to get whatever I needed for my child. Aidan was born healthy, no thanks to her. Yes, she got me to the hospital every time I had a bleeding problem while I was pregnant, but only because if I had serious medical problems it could go back on her.
After my son was born, I still had to have several doctor's appointments for stitches problems, migraines, etc. I asked her to watch him a few times for me. She always said she would and then cancelled at the last minute.
Throughout this, I dealt with a lot of yelling, telling me I was useless, calling me names, etc. Now this woman has called the State Police on her parents and her grandma saying they are in touch with her Uncle Randy, who is a runaway from the police on a crime his roommate in a halfway house framed him for. They have heard from him twice saying that he was okay, but immediately losing contact after that. Tell me, what kind of person does this just to get back at people for not helping her get her boyfriend (she's married by the way) to live in the same town as her? Right, I forgot to mention she's admitted to cheating on her husband three times at least. I called her out on everything she's done, and she's denied all of it. I tried to cut her out of my life, but it does not work. Everytime I get close, she does something else like this.
It's time for her to grow up and realize what kind of life she's living. What kind of mother tells their 9 year old "I hope your grandma dies."? She's done all of this stuff and still thinks that everyone should worship the ground she walks on. She's destroying lives and she doesn't even care. I just wish I knew what to do about her.
Thanks for listening,
Ruth