Isn't "the group" for this event the entire class? I mean, what if the coolest of the cool decide FD and her friends are unwelcome participamts and that they msy not dine at certain tables or talk to others? Doesn't attending prom indicate thst you have agreed to a social contract that involves being cordial to people you don't otherwise hang out eith? If you wanted to restrict it to just your group then wouldn't it be best for the group yo go somrwhere alone?
I don't think that anyone is advocating that OP's DD not be cordial. But there's a difference between being cordial and letting someone that you are not otherwise close with glue themselves to your side for several hours at a once-in-a-lifetime event and prevent you from enjoying said event.
AG has already proven that she will try to monopolize OP's DD, to the point of literally running after her if OP's DD tries to walk away. That's not normal. And how does the saying go? 'The best predictor of future behavior is past behavior.' AG has already said, point blank, that she intends to hang out with OP's DD and her friends. Based on AG's own past behavior, the other girls can guess what that will entail, and they want to head that off.
OP, could you clandestinely go to the school guidance counselor and ask him/her for advice? Tell the GC that your DD is torn, but this is a memorable night for your DD, and she's dreading it b/c of AG at the same time as she's anticipating it. You don't even have to tell the GC who AG is, but just ask for advice on how your DD should handle it. Be sure to mention the Homecoming incidents, and say that you're looking for how it can proactively be handled best so that the Homecoming chase doesn't repeat itself. I mean, you/she obviously need guidance, and this person deals with the high school mentality, so he/she might have some useful advice. And you wouldn't necessarily have to involve your DD; you could relay the info back to her.
I was friends with a couple of other girls my freshman year in college. There was a socially awkward girl who kind of latched onto us. I'd forgotten about her until I read this thread. We didn't want her to be with us, but we, like OP's DD, didn't want to hurt her either. We just ended up ditching her sometimes and making secretive plans, and tolerating her when we couldn't. Not the best option, but it was easier b/c it was a big campus and there was nothing as formal as a Prom to worry about. And it didn't last long b/c it was toward the end of the year.