So, as the title says, a close friend of mine vented to me that she was molested almost a year ago by a guy who's a year older than her. She's 13 (middle schooler, 8th grade. Let's call her "Diane") & the guy is 14 (highschooler, 9th grade).

She hasn't really told anyone else about this. She said she did, but they brushed it off. I didn't ask who or what they said. I avoided asking for unnecessary details and just did my best to listen to what she what she was comfortable telling me.

I'm 21. (She's technically my younger siblings' friend).
So their highschool/middle school business isn't really any of my concern. But I take predators, molesters, and rapists seriously. I'm concerned about Diane's safety as well as my siblings' since they all go to the same school.

Diane doesn't want me telling anyone about it though because she's not "emotionally ready" and she just wants to move on from it and live a normal life. I understand that but I also think that the guy should be punished for it.
I'm afraid he'll do it again. though she assures me that he wouldn't.

Telling someone would be betraying her trust in me. but she wouldn't have told me if she didn't want help right? or am I just presuming too much?...

(she's not really close to her parents. she doesn't think they would understand and she's afraid of how they'll react. I don't want to go into details but her home life isn't ideal).

Tldr; essentially my dilemma is whether I should tell someone about it or not. and who.

Tell her to fuck off and think about the shitty dilemmas she puts people through because she feels uncomfortable about something that happened a year ago.

Everyone has their moment of weakness. She's generally a happy person and I've never seen her sad. Which is why this is a shock to me since all this time, she's just bottled it up and she feels like she has no one to listen to.
I just want to help her in some way but I'm not sure how. (I'm not very good with people >_< )

Thanks for your input though, NZPIEFACE