I don't blame you.
Keep your eyes open, because things are going to get hairy. Young folks have a tendency, especially the macho ones, to fight before they think...to use violence instead of diplomacy.
The young man in Apache Junction has already received death threats and your sister's experience says that her classmates are just as liable to do something stupid.
Don't be afraid to trust parents or other adults who you know.
The good news is this sh-t would not happen at my private high school. The good news about such institutions is that you can "control" who can come in and stay in. Public schools have to take everybody.
So, since when is burning a foreign flag arson? This is insane and speaks of another agenda.