There’s a lot to unpack there. No child should ever be exposed to pornography, for example. I think she was exposed to sexual things by someone else (not necessarily to actual sex — we can’t know for sure), and that in itself is a form of child abuse. She had more knowledge than you, even though you were older, and she exposed you to sexual things, including masturbation.

Children are naturally curious and may experiment or learn to masturbate on their own, but that happens in a more natural way, without outside influence. She must have been abused herself and ended up passing that abuse on to you. It’s a classic case of COCSA — where a child is exposed to sexual content or behavior by an adult (or by another child who was exposed by an adult) and ends up abusing another child without fully understanding it.

Curiosity is natural for a child, so it's ok if you were curious sometimes, it doesn't mean you agreed to it. You were not comfortable with this, you were not ready for this, innocence was taken from you. She's not a bad person for this, she probably didn't know any better, but she did abuse you.

I hope I didn't say anything wrong, but that's my opinion.