Don't pretend like you know a 16 year old, because nobody does. After spending my high school career with a group of friends of which the majority were girls and having gone out with a girl for 9 months, let me give you this piece of advice, prepare yourself for anything.
It is a pretty big generalization, but I'll say it anyway, it is impossible to nail down the psyche of a high school girl. I've seen my girlfriend of 9 months (one of the sweetest girls I had ever known), go out of town, come back, and profess that she got drunk and cheated on me. First time she had ever had a drink in her life, outside of wine with the family on New Years and she never showed even the faintest of signs that she was the cheating type, and I guarantee that I knew my ex better than you know this girl.
However, I am not saying that she has cheated on you, or that she will. Just brace yourself for anything, and NEVER say that she wouldn't do this or wouldn't do that. Because even the best of girls are capable of commiting acts of great bitchery that can leave even the strongest of men with a huge "WTF?!" aftertaste.