Wondering why I didn’t walk away from this SA experience, and what that could tell me about my relationship with my mom at that time

ETA- I have a 3 year old and he will tell any adult ‘no’ if they try to tickle him or pick him up when he doesn’t want to. It’s just hard to believe I didn’t feel that same autonomy

Trigger warning for sexual assault

Please please don’t be mean, I’m scared to post this but hope someone can help me with some advice.

I was in therapy with my husband yesterday (we see someone to work on communication issues… lol) and the topic of intimacy came up. The therapist went that direction and asked us what our earliest intro to sex was. My earliest memory of it was a sexual assault that was ongoing for I think a year, or years? I’m not sure, I was like 4/5 years old. It was something my older sister told me I had to do with her every time I showered. She told me to shower with her and then while in the shower she told me I had to choose between doing one thing or another, both sexual acts. I did not want to do either and asked her if I could not. But for some reason I felt I didn’t have a choice. The bathroom was in the middle of the small house and it would have been hard for my parents to not hear me telling her no.

The therapist said that older siblings teaching younger siblings about sex and stuff is normal. My sister also taught me what masterbation was when I was 4 y/o and I was happy with it. But what she said stands out about the shower thing is that I didn’t want it to happen, it was ongoing, and it was upsetting.

My question is, why didn’t I just walk out of the shower and bathroom? Why didn’t I ask my mom to make her stop? I remember I would always ask my mom ‘(sister) wants to shower with me, can I?’ praying she would say no so I could avoid the situation. But for some reason i genuinely didn’t feel I was able to or allowed to tell my mom I didn’t want to.

For background, my parents divorced before I was born. I was unplanned and unwanted as I’ve been told. I have older siblings my mom had to care for, and I don’t think I got much attention as a baby. I don’t have a relationship with my mom today because she told me she wishes my children will torture me like I tortured her, and that she will become best friends with them and make them hate me. Basically, she’s nuts, but she’s also an elementary school principal and very well respected in our community, so it’s hard to believe the things she says/does to me in private.

My sister was/is an ‘externalizer’ for those who have read the books, a type A personality who my parents never disciplined for fear of her retaliation. I think she became that way bc of the emotional neglect from our parents, but who knows. But I can’t really imagine I picked up on that at 4 years old?