My dorm-mate is a man-eater...?

I have a little bit of a problem with my dorm-mate and once good friend. I've known her for about 3 years and I've seen more and more things that I do not like. She is a habitual liar and will lie over the most petty things and will also make up the most ridiculous stories (I am uming to gain attention). She also likes to turn the story around so that she looks like the victim when in reality it is her causing the drama. She is very flirtatious and it seems that any time a new guy joins our group of friends, she has to pounce on him, even if she is not interested in him. She has done this to several guys, leading them on and stringing them along and then talking trash about them behind their backs and then being so flirtatious and friendly to their faces. She caused a huge riff between my best guy friend and I because she was manipulating him and telling him things that were untrue to make him not want me as a friend anymore. She complains constantly how everyone seems to be in love with her and how "annoying" it is and how they don't "get the picture" and it is very frustrating. If you don't like someone and you don't want them to like you...why are you grinding all over them?? She is cute, don't get me wrong but last time I checked she didn't look like Megan Fox. This is very hard to live with and see on a daily basis. She also will put me down in front of our guy friends or other guys and I do not understand why. Anytime I have been interested in a guy and they mention their interest in me she will tell them that I am not ready for a relationship and I still need to heal from my last one. What really threw me over the top is that recently their was a guy that I became interested in. I told her I thought I might like him and today behind my back she went and asked him out. I feel like I'm in high school. It's ridiculous and I feel like I don't even want to be around her anymore because this happens all the time, I don't know what else to do. Am I wrong to feel this way? Am I overreacting?