I'm sorry she's acting like this, and I definitely don't agree with the people who say that you're overreacting and to leave it. It's understandable that you're really upset and her behaviour does seem really callous - saying to kill yourself, wtf?!
I would speak to her on the matter in a sensitive way, if you can. Just sit down with her and tell her how much it hurts to hear her say those things and joke about them. Just be polite and calm. If she carries on, I think you could either go two ways - report her to a teacher and try to have a talk with her where the teacher mediates (which can be surprisingly helpful), or tell her that she has been hurting you a lot and you're really upset with her behaviour, try to stick out the two weeks and then you hopefully won't have to communicate with her as much when you finish.
It could be her coping method if she is suicidal, yes, but it doesn't give her an excuse to hurt other people. I have similar coping methods sometimes (more like taking the piss out of myself, but whatever) and if it's hurting another person, I will always stop because it's rude and selfish. It could also just be that she hit "that age" late and is deciding to suddenly try to be ~*edgy*~ by making jokes about 'dark' things.
However you choose to deal with it, I hope it all goes well.