You need to tell her.
I hate to be the bearer of bad news, but she's probably picked up on your feelings already... us girls have a knack at it. She doesn't reciprocate the feelings if this is the case.
But the thing is, when you tell her and get ultimately rejected, you WILL be able to move on eventually, and still possibly have her as a platonic friend. It'll be better than hanging in limbo because you're too scared to say anything.
I could be wrong, though... sometimes girls get quiet when they realize they like someone that's THAT close to them. I wouldn't get your hopes up, but it's a potential.
BUT STOP HANGING IN THE MIDDLE. YOU'RE GOING TO PROLONG YOUR SUFFERING IF YOU DO. RIP THE BAND-AID.