Never underestimate someone who threatens suicide. This is mental illness. I'm not saying she's crazy. There isn't the same stigma attached to this anymore. She may have some sort of chemical imbalance that can be fixed with therapy or medication. She will hate you for a moment but you need to tell her parents or a counselor at school. It's the only she will get the help she needs. You can't deal with this by yourself. Put you ego away because it's not about you. Go get her some professional help. You in over your head.

If she's seriously suicidal she needs professional help. This is the only way she will ever make real progress with her depression. You aren't a therapist and shouldn't try to be. I think you should tell her that if she really cared about you she would try to get better and see a doctor. It is not fair of her to burden you with problems you can't fix.

If you ever feel she is in immediate danger of hurting herself, call her parents or the police.

Maybe you should be more serious about her and if you love her and want to be with her then tell her and then ask her to marry you,I'm sure she will be so happy that she will never think about suicide ever again.

try to be her counselor without her knowing. she might have this thing called depression my dad has it. it kills them slowly but if she takes these special pills, she will feel really happy and stop having these thoughts.

She needs to see a docter or talk to her mother if this is serious. You must persuad her

oh dear i feel your pain brother

once they have that mindset there is very little that can be done