I know this sounds simplistic, but she's still very, very young, and she may well just... get over it.
That is what happened to me. In my early 20's i was appallingly self-indulgent and negative about everything. Nothing anyone said went in, cos i thought i knew best.
I still think that, but i'm not as depressed now!
As i got older i just realised how lazy i was being, not making any effort to change stuff that was making me depressed. I'm much more 'Terminator' about getting stuff done nowadays. It's helped a lot.
... still get depressed at times, but it's less of a constant now, more of an up and down. Which is dealable (made up word!).