Something I cant forget

When I was a kid I molested by my older sister were 4years apart. I dont know if she thinks I forgot or idk but it's been really eating at me I didn't think about it too much when I was younger but for the past few years I think about it almost daily.My sister was molested by a cousin of ours when we we were younger but that's no excuse to hurt anyone let alone do that to your little sister. These thoughts bring so much emotions out of me and I'm starting to get angry when she comes around and just annoyed and disgusted with her presence. I try to tell myself she was a kid too and was just confused too but idk .I know she isnt that person anymore and it's been about 20 years but I cant let it go . I have never told anyone and probably never will other than a therapist. I have a 8month old son and she gets upset at the fact I won't let her watch him and basically called me a loser for it but how can I let her watch him after what she did she wont ever acknowledge it or at least pretend to know why I wont let her watch my son and its makes me so angry because I'm trying to protect everyone by not ever bringing up something that causes me so much pain. She forever has scarred me I hate the way I feel