Why does this girl keep annoying me ?

She is teasing you because of the reaction she gets from you. She realizes it gives her power and she is also entertained by it when she gets a rise out of you. I suggest that you just plain ignore her. If she gets in your face give her a dirty look and walk away without answering. The teasing will probably get worse for a while but will end after she sees she isn't going to get anything out of it. You don't owe her a response or an answer, and it doesn't give you any power to react, you just lose more dignity and power. Don't try to make a friend out of her either it isn't worth the trouble.