This chick doesn't sound like she's depressed. Sounds more like a hormonally driven teen who is trying to manipulate the guy into getting back with her, and yeah she could actually end up harming herself in a fit of rage. Any way, do what everyone else has already said - tell her parents or a teacher, someone who will actually take the steps to make sure she gets help.
I'd suggest cutting off all contact with her after doing so, no email, instant messaging, txts, calls, whatever. Since she's coming off as being a manipulative kid, as long as you're talking to her, she's going to think she can still get you back.
XI Wiki


