How do you deal with an annoying friend? Quite long, sorry!?

Okay so there is this girl (I'll call her Emily) who is pretty much one of my best friends. But recently she seems to have gotten REALLY bitchy. Whenever I talk to her these days it's ALL about her- she only ever talks about herself and if I try to get a word in edgeways she goes all quiet and gives a really short response before changing the subject back to herself again. She is really pretty, and I mean BEAUTIFUL, but the thing is, she definitely knows it! I mean, I'm not a jealous person, so this doesn't bother me, but on a regular basis she'll come out with stuff like: "OMG your eyelashes are SO short compared to mine!" or "Hahaha you have bingo wings!" (She is also pretty skinny but has an awesome figure). And basically it just makes me feel like sh*t. She is also one of these people who is always on a high horse, she always calls us immature and acts embarred to be seen with us. But most people don't see these sides of her, so she is pretty popular (surprise surprise).Up till a little while ago I just blew most of this crap off, but recently she has gotten soo much worse. One of my other friends (calling her Kirsty) in our group really, really likes this guy (she gets really depressed over him) and Emily actually deliberately went out of her way to make friends with his whole group, and flirt with him till he fancied her, even though she told me she thinks he is disgusting, she told me she only did it to mess with HER FRIEND, because she thought it was really funny when Kirsty got all depressed, and she gets a kick out of making random guys like her. So this dudes heart is now crushed, along with my other friend. Also, her very best friend (calling her Fiona) likes this guy (who has a girlfriend) and Emily has recently decided she likes him too and is flirting with him A LOT. I'm getting kinda worried that she is gonna do something to me soon, and I'm uneasy about being friends with her. Kirsty doesn't talk to her anymore and I kinda wanna do the same, but I don't want to be a b*tch. So what do I do? Ignore her? Stay friends? Does it seem like I'm making a mountain out of a molehill so to speak? Please help, not sure how much longer I can put up with her!