I’m confused. So when you were 6 years old, a fellow 6 year old molested you? Or was it the 6 year olds mom? And if it was that 6 year old she was or had been actively abused by her father?

I think there is a natural curiosity at that age that had been twisted by the abuse of the girl that lead her to not know what was appropriate or acceptable. If your mom just heard that her 6 year old kid was in a cupboard with his pants down she probably assumed it was willing and that was where her frustration was coming from. Embarrassed that her son exposed himself to a girl. Especially in the moment when she didn’t have more information. That doesn’t make it okay at all, but it might be a more normal initial reaction than you realize.

That said, you have deep feelings and frustration here. And it needs to be addressed. Especially if you haven’t found a way to really get her to understand how deeply you have been hurt by that incident and her reaction. I’d try to find a counselor (there may be some free options) to talk through and sort your feelings first. If you can’t at only 16 then maybe try writing your mom a letter explaining that 6 year old situation from your eyes. Share your fear and feelings in the moment. The loss of your innocence and the hurt and confusion you felt later. You can address other issues, but it might be good to focus on the one issue. Let her read and then raise the issue. Try to keep the letter on you and your feelings rather than attacking her response. If she does anything other than respond with compassion and apology then i wouldn’t waste time confronting her further. I’d just accept that she will never give you what you need and deserve on that front. But if she does respond with compassion, then use that as a springboard for honest and open communication about other issues and try to work through them with her to reach a better place where you feel heard and safe.

Good luck and I’m sorry you had to go through it all.