It has been a while since I read this story and I feel like the details are fuzzy. But the gist is a woman enjoyed hurting people in middle school/highschool. She later meets a friend she knew and it turns out her friends is into the same thing, and actively does it. This friends introduces her to a session where they rape and torture a girl.
I've been looking for this story for quite a while now and don't know where else to turn. I'm fairly certain this is where I first read it but it's possible I could be wrong.
Any help is appreciated.