I wouldn't make it too serious at first, so you'll still be friends no matter what.

Oh, and we'll still be best friends no matter what so that isn't an issue, and don't even say that I don't know that, I know, it's none of your buisness!

I think you should at least ask her out, I mean I had a lot of crushes on my friends, and I regret asking them out, but yet again I'm so shy, but anyways yeah go for it, and if she says no you'll still best friends.