Depends on how she treats you. I am 17 and have done both of the following:
If she calls you whenever something happens, tells you details about other guys she likes, and truly treats you like she would a girl best friend, then it is nothing more than friendship.
But if she refers to you as a best friend, and you guys hardly talk about anything that she has going on in her life, and rarely hang out. She may like you. Also, she might want you to think that you guys are closer than you really are. She could be expressing that she really trusts, and enjoys being around you as well.
The possibility's are endless, but if you really want to know when a girl like a guy, they basically do the same things guys do when they like girls. ie. Go places where they know they are going to be. So think, if she is acting like she likes you, then she probably does. :)
from the original question, I would say that it is a tricky situation. but judging by this update, I would say she def likes u! any girl that wants to get close to a guy, in any way, has some sort of attraction towards them...and the fact that she never talks to you about other boys can be a few different things. most likely, its because she does like you and maybe she can tell there is something going on between you two. so she feels that if she mentions other guys, if these "other guys" even exist, then it will make things awkward or it will turn you away. overall, I think you have got a shot on this one! good luck :)
I think she could think of you as more than just a friend, maybe not now but eventually. My best guy friend I never in a million years thought I'd like him, but a couple years ago I started to like him. It's the closeness you two have that makes her like you more, or for that fact make any girl like any guy more. Shows you care and listen without being in a relationship with her. Though this is all true and I can agree with the other girls statements, I also can agree with the guys. If she is your best friend you have to ask yourself, do you really want to get into a relationship with your best friend? What will happen if it doesn't work out, depending on the reason you two could end up hating one another, then you would not only be single but you will have lost your best friend.
You still have a chance, if the relationship is still new. If you've only known each other for a couple of months, there is always a chance her feelings could change the more she learns about you, but if you've known each other well, and pretty much inside out, then I doubt there is a big chance of her changing her feelings.