How much time would this person have to serve if they did this?

For my short story,the main villain has threatened to bomb her school. The principal is dead, and the faculty ditches the students and leaves them to die by locking the front gates(the only exit). The villain makes an offer to the trapped students she will let them go if they kill the main protagonists. In a panicked frenzy the students do as told and try to exterminate the main trio. The most intelligent of the three has made the discovery that there is no bomb,and the villain was lying through her teeth. So after a big fight scene with the lead protagonist,the villain is defeated and the authorities finally arrive. Long story short, the villain is 16,so can she be sentenced to an adult prison?And under what charges?I know attempted murder and manslaughter is two of them but what about the hoax bombing?Anything?And in the end,will she be doing a life sentence or if not,how many years is she in for?