Actually, I don't think we even know that. It seems that she died of something and they disposed of her body, which certainly indicates that they felt some guilt in that outcome.
But whether they killed her, and certainly intentionally, has yet to be seen.
Exactly so. They may have been experimenting with drugs--she had a bad reaction and died--Who knows. Lots of 17 year olds would panic and act stupidly if that happened.
Good point.