find other good friends?
suggestions above are good, she can also take up a new hobby and course and meet new people there?
oh, and if either one badmouths the other when not present or complains about the other one, she can say something like, 'Tell that to her.' Or, 'She's not here right now so I think it's better if we talk about something else.' and/OR just change the subject.
Someone told me she straight out told her friends/acquaintances to not talk badly about someone else when not present. I think that's better than listening to any complaints over that person, because if you do listen, you start wondering, 'hmm what if she's right?' and looking for those traits..
And then a while or a few years later that person may decide to LIKE or admire that other person uggh!! (and wants to make friends with her etc) So, tell her to not take it so seriously!! (It's tough, I know, I ended up distancing from both groups, kinda, though I later regretted it somewhat..)
Does she have to be in same space with both of them? (like going to classes together) She could maybe divide classes so that she's in some classes with one, some classes with the other.. sometimes going shopping or for a drink or lunch with one, sometimes with the other, etc. It's really important that she doesn't let'em trash each other, imo. There are soo many more interesting things to talk about! (And if they don't know any, why is she friends with them?
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They can agree to disagree, 'armed truce' or something like that.
Maybe the friends are jealous of each other and any time she spends with you too.. has it gotten worse since she started dating you? In that case a small speach how they will always be good friends etc might be in order. She can make it clear how she hates that kind of behavior (trashing each other etc) and she can just leave when/if they start behaving badly again..
On the other hand, does she know their reason for hatred of each other? If one of them stole another one's bf or something, I'd consider that highly unethical and would question myself if I want to hang out with someone like that. If it's just bickering and jealousy, then she can try the above suggestions..