I used to interpret dreams. Usually, when you dream about someone else—I'm assuming this girl is someone you know—you're actually dreaming about yourself. In particular, you're focusing on characteristics of the other person that you see in yourself that strike you, or that are your focus at the moment.
Incidentally, though some dreams are literal, and others are predictive, most dreams are less about the obvious and are more symbolic. Elements within them serve as metaphors for issues that are prominent in your life at the moment. I hope this helped a little.