So... to be clear, how well do you know this person? Are you good friends? Close friends? How much do you know about them?
This attraction, is it just chemical? Is it your pupils dilating upon studying her face? Is it your heart pounding when your eyes meet? Or is it those things, and also that you can speak to positive things about her personality and interests?
I think these are the questions you should ask yourself before you decide you really like someone. You may be of an age where it can be difficult to differentiate between an infatuation and something deeper.
If you don't really know the answer to these questions, that's fine too. Have you considered simply asking her out, to help you to get to know her better? She may handle that maturely and just say she's not interested. If she's not as mature or if she has other problems she may be dealing with, she may get really weird about it. I guess that's the worst that could happen, but either way, a no is your answer on YOU should do about it: do your best to move on.
She COULD also say yes.
That would be interesting, wouldn't it?