I know she can't help it but...?

OK Long story short. First my friend and crush sat next to each other in social studies, now the teacher puts them in the same group together. Today, we switched seats in science and she sits right across from him. Whenever I turn around she's always laughing and talking to him. It's almost as if she's flirting. So I told her once or twice how this makes me feel. I mean, she knows how much I like him. She rushes to claim it's not her fault. But she keeps twirling her hair and giggling. So when I start to avoid her, she becomes the upset one and asks "Why are you mad? I didn't do anything!!! It's not my fault!!!!!!!!!" So...what should I do? I've tried talking to her, I've tried avoiding her...any advice?