[Jaguar]

First, no hate. You're doing the right thing by getting all the advice you can.

I don't think there's any choice but to tell her parents. They're going to find out anyway soon enough and if she goes missing as a runaway she exposes herself to all kinds of bad shit including rape and murder. You already understand you have to do all you can to prevent that.

Yeah, she's not going to like it, but like you said she's not making rational decisions right now. She's young and from what you say, immature, and she's going to need a lot of help. There's no way she can deal with this herself no matter how much she thinks she can. After her parents know, all you can do is be there for her and give her as much support as a loving cousin can.