Why was his friend being a ****** to me?

So my bf is french but we both live in australia. I met some of his friends who are french too, for the first time the other day and i got talking to them, his guy mates were really nice and friendly, but there was one of his girl-friends and she was such a biiitc hh. They can all speak english but every time i would say something she would start talking in french on purpose so i couldn't get in on the conversation. I even tried making a conversation with here, and she didn't want to know. Why would this be? I mean i know she doesn't even like my bf because she has this guy, but why so rude?