My fiancés Mother is OBSESSED WITH ME!!

This is more of a rant but all advice will be appreciated.

My fiancés mother will NOT stop talking about me!! She is completely obsessed with me and it’s gotten to the point where I want to bawl my eyes out because I cannot get her to leave me alone!! She calls and blows up my fiancés phone to talk about how I’m a whore, I’m using him for his money, and that I have stolen from her. It’s been going on for an entire year. She used to blow up my phone every two weeks until I finally blocked her number. All her kids have stopped contacting her and visiting her because the conversation will be about me the entire time. Why??? Why won’t she let me be??

It all began when I gave birth. She used to be such a sweet lady, I loved her, until my daughter came into the picture. She smothered me and wouldn’t let me learn on my own. Always had something to say about EVERYTHING. When my daughter turned 1, it only got worse! I stopped letting her babysit because she told us she wouldn’t babysit unless we listened to her parenting advice and when we told her it was best she didn’t take care of her, it was like I had betrayed her. All her kids tell her to stop and leave me alone but it only makes things worse. She wants them to hate me & attack me. My fiancé has cut communication with her, the only time he’ll talk to her is to tell her to stop blowing up his phone. We had his younger sister over for drinks a week ago and she told me her mother only calls her to cry about how they should listen to her and hate me. She also confided in me that she thinks her mother hates me because she wanted to raise my daughter and I didn’t allow her to. I’ve tried to message her to move past all of our drama and I’ve pleaded with her to just let me and my fiancé live our lives but I only receive paragraphs of pure profanity and threats. She’s pushing everyone away because of me. I feel fucking awful that her hatred for me is the reason none of her kids want to go see her. They’re tired of hearing it. What can I do to get her to stop? I’m not afraid of a 5ft skinny old lady but I know the extreme lengths people will go to when they are unstable and obsessed.. especially now that she thinks her kids are “blinded” by me. A small part of me is afraid because this is not normal at all...