I know this is slightly off topic, sorry, but it does annoy me a little bit when teenagers say things like relationships shouldn't exist young, and you're just going to break up so what's the point, and you shouldn't commit young.
While to a certain extent, this is realistic thinking, it's pretty depressing. Not everyone has teen/young relationships, I know that. If it's not by choice then it just means nobody good has come along yet or they aren't much interested in the opposite sex, nothing wrong with that. But I don't agree with the notion that young relationships serve no purpose.
They serve plenty of purpose. Gaining valuable experience, developing certain skills and making later relationships smoother and easier, understanding the opposite (or same!) sex in a romantic way, and most importantly spending time - however little or much - together and being happy with a person for that time. Plus, you could go on to spend years or a lifetime together, who really knows?
That's my 2 cents anyway, little rant for the morning. As to your problem: I'd be straight with her, telling her you really like her and would quite like a romantic relationship, or at least an establishment as to the status of your current relationship. Just talk it out. Being a girl, I know we say stupid things sometimes when we're desperate to act all cool and casual, but really want the same things as the boy. You never know, she might be hiding her true feelings.