I think you should consider what her feelings are and if she's happy as she is now, so be it. They might not last forever, so you'll always have a chance. I'm not the kind of guy to purposely try to break my two friends up just to be with one of them, but I really don't know how bad you feel for her. Well, the bottom line for me is, if I really like someone, I want them to like me back as much as I do to them so if she does have feelings for you like you have for her, then I say give her a few nudges here and there and see what she thinks about it.
Sorry if I didn't really help you, but either way, best of luck!