How well do you know this person? Does she respond positively to your words, your smile, your touch? If you continue to get good vibes, then you -- believe it not -- ask her.
There are generally some little signs that show when someone likes you. Does she lean into your personal space when you are talking? Does she touch your arm or leg when talking? Is she a bit flirtatious? Your best bet though is to communicate your feelings and ask her.
