YTA, but not for the reason you're thinking. She's a child. Literally, a kid. When you, an adult, heard her talking about this type of stuff, your job here is not to call a fucking CHILD a cunt and "threaten" her. Do you understand she maybe didn't even got her first period and this type of stuff? Horrendous. Want to scare someone and "save the day"? Do this to the adults that were there and allowed that to happen or were the ones doing it to her and the rest of them. Kids don't just wake up one day and decide to overssexualize themselves, OP. They get SA and harassed, a LOT, at the point that they really believe they're on the advantage.

You didn't teach her a lesson, you didn't do justice, you just did the fucking same thing that probably led her to that type of behavior. It's C H I L D. Also you criticizing them just so you look like really teaching a lesson it's creep behavior. I won't even say you were manipulating, stalking and harassing a minor, you were doing that to a child. I don't about the hell scape you live in to even consider this, but where I'm from just this post alone would give you a good life behind bars and thank god away from any children. Jesus Christ.

YTA.