This EXACT same thing happened to me. I had some liquid Nitrogen for a science experiment at school, put it in a 20oz Coke bottle. Of course that's not something you do without knowing mostly what will happen, as I suspect was also the case with this girl. I took it to the bathroom (somewhere with no objects or people to damage) and it exploded, making a bit of noise.

I was expelled and charged with the same sorts of felony charges - constructing a bomb, detonating a bomb at a school, etc. With a small bit of lawyering the charges were reduced to one count of misdemeanor disorderly conduct for making a loud noise. For that I was able to get "diversion" (like a lighter form of probation for juveniles), just some community service and drug testing, and could have my record sealed at 18. I was not, however, able to successfully appeal my expulsion.

I hope that this girl will be able to get a similar outcome and not end up as a felon because of this silliness.

This was in the middle of my 10th grade year. My next two and a half years doing home schooling and at the only private school in the city that would take me were terrific, I am very glad my life took a turn the way it did.