Kinda helps that you were a guy, though.
Am I sexist if I call girls "unstable"? Especially around puberty?
YES!
With gender bias aside for a moment; take into consideration that during puberty it's a hard time for anyone. Your body is changing, hormones and insecurities run rapid. Clique politics that dominate the high school corridors, and the sense belonging is the only thing that seems to be concrete. Unfortunately it's hard on young girls because a lot of them are taught that they have to be a certain way for people to like them. And among females in society there isn't a sense of camaraderie like between males, it's a constant battle from the home, workforce, and through society.