Advice first: Don't go up and immediately ask if she's a lesbian. When people do that kind of stuff, there's usually a high suspicion that someone is bribing you to do so. You'll prolly get slapped or start a catfight.
It's not uncommon for straight people to hug members of the same sex. Straight guys hug me all the time .. and yes, they know I'm gay.
Now, my suggestion: Get to know her. Become good friends. Don't do anything stupid to make her dislike you, but don't be someone who you aren't. Keep your hormones under control and go slow. A steady friendship is much better than a random hookup. As you two get more comfortable with each other, she will eventually come out (or not).
Good luck
