Bitchy sister in law what to do?

Well this is my story, I have an awful sister in law who is also manager of a dental clinic, I was looking for a job so she offered me a position (this was 4 yrs ago) I thought she was so nice for doing this and I was happy my brother had met such a nice lady, but when I started working for her I saw another side of her that I didn't like, one of the employees complained to her that she didn't have her full 10min break and she was fired on the spot, also she was really awful to a patient and the patient ended up calling her a ***** and walking out, to cut the story short she fired me without warning, I asked her what I did and she didn't give me an answer I said repeatedly that I liked the job and if I could do anything to stay and she said no, aggressively, I asked her if it was the way I was working and she said no. To this day I don't know what I did wrong, or if I offended anyone. She is also a ***** to my brother, a terrible step mom and she never cleans their house! My brother and her fight a lot, her mother also doesn't talk to her, they don't have a relationship. I don't enjoy Christmas anymore because of her being there, she really sucks up to my Dad and he doesn't seem to see what I see. I don't want this woman in my life or part of my family anymore, I've even thought about moving away or taking my own life just to get away, no one else can she what a manipulating ***** she is! I've tried to explain this to ppl no one listens, my brother came over yesterday complaining about her, what can I do about this I am concerned about myself and my brother?