I can almost guarentee what happened is that while your daughter was gone she was the one everyone gossiped about, talked bad about, etc. It's a way kids "bond", by disliking the same thing/person. At that age, with everyone wanting to fit in, it's an easy habit to fall into (if you are talking crap about someone else then nobody is talking crap about you..etc) and a hard one to break out of. It happened to my daughter too and was really weird to witness. All it took was for my daughter to willing remove herself from the group for awhile (not to go overseas but to be involed in a school activity her friends were not a part of) and BAM! Outsider status. I'd like to tell you it blew over but it happened her Jr year and it didn't get better, partly because she knows how to hold a grudge, haha.. Her senior year had her being something of a loner and going outside of school to make new freinds and social connections. It wasn't until everyone was into their 20's and the "group mentality" was gone that almost everyone individually apologized for the way they treated her, and nobody can remember exactly why/how it happened.
The upside is that now she is considered really cool, one of the kids that didn't hang out that much, who went away right after graduation, so she's something of a mystery with an almost celebrity status thanks to FB, and always being called upon to show up to events and parties when everyone comes back into town. She rarely does
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