What does she mean by this? i need a girls perspective 10 pts best answer?

This is hard to answer since you didn't say what grade your in. You can go to Prom for both your Junior and Senior year. She obviously wants to go with you and to know what you are wearing so she knows what shoes to get, however I don't think she wants to believe you are going with her only because this is your only chance to go. You should say something about really wanting to have fun with her while your there.