What should I do about my cousin?

Recently my cousin had got a boyfriend and she is acting like she is better than my best friends and myself. Her boyfriend is trying to tak to us and we still try to be cool with her but she doesnt try to notice us unless she being smart acting as if she doesnt know our names and we used to be close but all of her friends stopped talking to her once she got the boyfriend and thought that being around her real friends would be trouble.... Little background history when we would go out she would get out and throw a fit because guys would come over and hang out with us. What should I do about her because usual I would go up to her and start a fight but I am to old for that and I am trying to handle it the right way.