I never told anyone a classmate was being SA by her father

I’ve literally never told anyone this before and this happened when I was in grade 2 in the late 80s. A girl in my class said she wanted to show me something during lunch break. She said it was something her dad did with her called “rocking”. I won’t go into too much detail as it makes me feel sick just thinking about it. But basically it involved being in a bathroom stall with no pants, and a rocking motion. We did this for a few days during lunch breaks before I said I didn’t want to do it anymore. I didn’t really think about it again until I was an adult and then with a shock I realised what it actually meant. I was an odd kid and pretty clueless, which is probably why I didn’t think much of it. And as much as I try not beat myself up about it, I can’t help but think that if I had just told an adult, perhaps something could have been done to help her.