This whole flashback creates a pretty interesting dynamic. Like, it kinda makes her both more and less sympathetic at the same time. Of course what happened to her was incredibly cruel and disgusting, but at the same time, having experienced these things firsthand, she has all the reason to not inflict them on someone she supposedly "likes". That makes her just the same as her bullies.
Potentially even worse, since she was in the unique position to know exactly what it feels like to be on the receiving end, and still went through with it.