HOW do I get rid of the girl thats in my way of getting to the guy I like? HELP PLEASE [guys or girls]?

I have liked this guy since June. my stupid skank of a cousin went out with him from July to a week ago Wednesday and had a nasty habit of dumping him once in a while. this killed me of course because i care about him. this time she has dumped him "until senior year" so they are "just friends." I want to make a move on him, but yesterday, we invited him to our cousin's wedding with his two cousins (one of whom goes out with my sister)...I told him that I like him about a month ago (the last time she dumped him.)...but anyway, yesterday, at my cousin's wedding she is all over him and like rubbing it in my face that he likes her, even though she doesn't really like him...since she clearly is too self-absorbed to care about anyone but herself, I don't really care if I hurt her. Now, the question is, how do I get rid of her?