How Do I Relate With An Unfriendly Mother inlaw?

How Do I Relate With An Unfriendly Mother inlaw?

Good morning Aunty. It's not as bad as the title sounds o. Let me explain. I've honestly been totally good and generous to my fiance's family. By nature I'm very friendly and I talk to them and I make them a part of my life, not just like people I have to interact with because I'm dating their son/brother/uncle /nephew.  I participate a lot  in family activities, we talk, I will do them favors sometimes. It seems like everyone in his family likes me except for his mum. 

I don't know why but from the moment I step into their house each time, I'm her target. She will randomly blame me for things

I didn't do and get really upset over it, shows that she doesn't want me in her house or something.  sometimes she will actually yell at me! andI don't know why but I tend to start crying when people yell at me but when I cry in front of my mother inlaw to be, after being verbally attacked it like makes her even angrier. She never apologizes afterwards...even after she realizes I didn't do what she thought I did. She'll just be like "oh ok." and carry on like it doesn't matter whatever she just did to me.

My fiance has defended me and stood up for me many times and they have gotten into arguements over me which I seriously hate being in the middle.  I have never yelled back or had an attitude with her. All I do is get anxious and emotional , drop some tears and my boyfriend comes to my rescue. I've never even openly expressed anger or hatred towards her or said she's mean or anything in front of anybody. So,  obviously,she has a problem  with me coming to visit or just doesn't want me around her son. the closest thing to rude I have said about her to my boyfriend (or anyone else) is "I think she is wicked to me and I don't know what to do." I'm already the innocent one here but I've been playing it up too a little bit more to keep my boyfriend on my side just in case she tries to brainwash him.

 For example, I'm thinking that, if I continue to act sweet to her and never trash talk her then no one can see me as the bad girl, if I don't blink or roll my eyes at her, no one will see me as bad. The more of a sweetie I am who doesn't fight back or say things about her the more of a bad person she looks and I will always  be totally innocent in everyones eyes. I feel like I need to do this because she's family and I'm not yet. Therefore my fiance and others in the family will always lean towards choosing her over me but, if I can look innocent enough by not contributing then maybe my Fiance will feel more inclined to side with me. Because the moment I talk back or try to defend myself, I am no longer the innocent victim and I become part of the wahala and he will be less likely to side with me in every situation.
Am I right acting this way or should I stand up to her bullying give her a piece of  my mind even for once.?