Dont you also think its kind of babyish to be having cliques in 12th grade?
Rule, there are some people who thrive in a cliquey relationship, and don’t give it up. As odd, and totally immature it might seem to the people looking in, that’s the way it is. Maybe its like an ego thing, like “I have something you dont…”?!
About the OP, I know there are some classes that got together and made shtick so that way, when it came time for weddings, no one needed to rent (something I’m assuming that would come in handy when a girl gets married after some friends are already married and paying rent), and maybe something more specific to the class instead of the standard fare. Another idea might be to set up a system where when Girl A gets engaged, Girls B, C, D are in charge of a shower/shtick. When Girl C gets engaged, Girls A, B, D do. Maybe doing something along those lines would get the idea that you as a class have a special bond and would strengthen it.
Good Luck!