Open Question: I have a family friend that both my sister and I talk to, but she has done some mean and hateful things to me?

and my daughter. This is how it started I moved back here from georgia and was staying with her. Instead of her being a woman and telling me she wanted me to move out she pretended that her landlord wrote her a letter to tell us we had to leave. Now my daughter and I was out on the street I was so sad and scared I didn’t want to go back home to my parents house because my dad drinks and was very abusive to my mother, I just didn’t want to raise my daughter up around there. But anyway I learned as of today my sister still talks to her and she was doing it behind my back. I told that if someone did my sister like that I wouldn’t have anything more to do with them. Her response is she is not her friend but she just calls when she need help or information about child care or how to run a daycare business. I was like but there are other people to call besides her. The problems here is should I be mad because my sister is doing this behind my back. Well so far I have cut all contact of with her. I think she is wrong.
If it was all that simple I would say squash it. But this has happened so many times with her I caught her a few times sitting over at her house. I going to class one day and see her car parked at her house she would have never thought I would so happened to ride by there on the way to class. Her excuse was she said she didn’t have to answer to anybody and she don’t like to be controlled. I told her she needed to let me know if she wanted to still be friends with her and if so then I will would know if I wanted to be in her life or not or have limited contact with her and when she needed help for her not to come to me. Let me decide if I wanted to be in her life is she wanted to talk to her to her anymore, and she needed to go to that person when she needed help not me.