I've read through the thread and it sounds like she needs some serious help. If you feel that telling her parents won't achieve anything, then you should tell you own if you haven't already (it's a wise idea, even if they don't know how to handle it themselves, they might know of someone who can).
I do have one question though - why did you rent out your friends house for a while, instead of using your own? (I can imagine you saying something to do with your parents, but you might have another reason).
[QUOTE= Stormtooper]Now, obviously, don't think that she won't attempt suicide, but don't have full belief that she will either. It would be best just to do what's already been said. Contact some authority figure, a school councelor, a cop, her parents. Most places have suicide hotlines that you can call if you think someone it going to attempt it.[/QUOTE]
I agree with what Stormtrooper's said here - get in touch with someone who can help in some way. Someone with a lot of experience in that area would be very useful here (the easiest way of getting someone helpful would probably be through a hotline).
To everyone else - even if some of you have bad feelings towards this guy, there's no need for all of these negative replies. It's a serious situation (especially considering the suicidal girl) and it should be taken that way. He's asking for advice, not for your opinions of how he's handling the situation.
EDIT - I re-read the thread through and most of you seem to think that she's joking around because she tries using a match to harm herself. That's definately not a sign that she's just joking around. There are many reasons why she could be doing this (trying to get his attention before trying something more serious etc etc.)