Why is my friend always saying how shes prettier than me, but she honestly isnt?

Okay, so, I have a friend, and I don't really like her, but I'm the only one who doesn't, well, just abandon her because I don't want to hurt her feelings:/ So, the reason why I'm writing this is because she has been telling me and her frenemies that she's prettier than me, but honestly she's not, well, the prettiest flower in the bunch lets just say that. You see, it all started when I first got asked out that she knew of, and it was someone she had liked for a while. Then she said, "wow why him i am soo much prettier than you" and ever since then she's had this kind of ego that shes way better than me, and recently, this guy I know was flirting with me and she kept trying to talk to him and shes a little weird so it basically freaked him out :/ p.s. im not conceited at all i just have enough confidence to know im pretty(: