I want to cut ties with my mother.

I need some help, or encouragement. There is so much to this I don't know where to start and would be here typing all night. Basically, I was at my mother's house with my kids on the weekend, sorting threw a bunch of stuff from my childhood She had kept. She wanted me to go through it all. This seemed to have brought up some memories. Memories, that I know are true and have always been there, but I never thought about them. After she and my Dad separated, she engaged me into some inappropriate sexual activity. It happened twice. I told her it didn't feel nice. And that was it, she didn't approach me again. I know these things happened. I was 9/10 years old at the time. I can't wrap my head around it. I know if I asked her why she did it, she would deny it. I think I don't want to continue a relationship with her anymore, I certainly can't leave my kids alone with her now and I just feel like I'm done. But I'm also feeling like I'm abandoning her and feel guilty. Im the only family she has. Her other children want nothing to do with her and she has no contact with her own family. Its always been me. The golden child who was always loyal and stood by her and never let her down.....unlike everyone else in her life. Even on my birthday, she wrote in the card that there aren't very many daughters like me left in the world.... I'm done. I feel like remembering this is the last straw, I could not imagine doing to my children what she did. I just don't understand it and want to cut her out my life, but I still feel concern for her. I don't know what to do.