Ugg! She is so rude to me! What should i do?

There is this girl, hilary. She is somewhat a friend of mine, but she always causes so much drama! And she is always saying that she likes certain guys, after hearing that i like them. For example, there is this really cute guy that i have 2 cles with, and about 10 minutes later, she walks in saying that she is in love with the same guy. (by the way, his name is seth) She has never met him! she states that they "shared a glance". This all happened about a month ago. I told her that she could go for it, because i knew she would be mad if i didnt let her. I have been talking to seth a lot lately, and apparently Hilary is stalking him! Anyways, i was looking for seth yesterday, and I asked one of his friends, and hilary happened to be walking by. She started talking to me, and was saying how she saw me and seth together, and how he must like fat and ugly girls, and how there must be something really wrong with her if he likes me and not her. (I dont want to sound bad, but she is way fatter and uglier than me.) Both Seth and i cant stand it! what should we do?