Risk it. Ask her out - politely and kindly, of course. There is no point harboring feelings for someone while continuing to be her friend. You will be stuck in a constant loop that you will find hard to get out of. Just ask her and she what she says. Don't make it serious or awkward and if she rejects you, be kind and wave it off and behave as normal. I know it sounds a lot harder to do, but remember: you have to risk it to get the biscuit.