You're probably not in the friend's zone yet, but you can't wait too long, or you'll get there. Make a lot of eye contact with her, it's a really good way to judge how she's feelin about the situation. If she looks into your eyes when you do, you should be able to tell if it's making her happy, uncomfortable, or nothing. If you think she's feeling it, kiss her immediatly. If she wasn't sure if she liked you, that'll probably help her decide quickly, and being as she's a good friend, the worst reaction would probably be an easy let down. I doubt that though.