OMG, I feel for you, your family, the staff and school members, and the poor girls family. Hearing things like this are really horrible. This scares me so much, being a high school student in Australia nothing like this has ever happened and i hope it won't ever in this country.
We had a victims father from the Colarado shooting visited our school last year and it was very depressing and tragic to think that someone that unstable would take out their emotions in such an unhealthy way. These horrible copycat trends are emerging among depressed/psychologically ill high school students, and really need to be stopped. I don't think these people understand the consequences of their actions. When a massacre occurs 100's of people are affected for the rest of their lives, how can someone be that selfish! and to commit suicide on top of that is a cowardly thing to do, if you wish to end you life, that your (debatable) prerogative, but don't hider anyone else's!
p.s. Yes, that girl was very stupid not to tell anyone but she was put in a really compromising position (her life and others) and imagine her frame of mind at the time. I would never want to be placed on any remotely similar situations, hence why I don't wish to judge her on it.