You are so afraid of losing her as a friend because you have romantic feelings for her too. You befriended her for the sake of your emotions and let me tell you this; getting amusing friendships is a fuckload of a lot easier than finding a good relationship.
Also, a good friendship is an excellent basis for a good relationship. You have only a friend to lose from trying, and if you lose one from trying it wasn't a good friend in the first place.
Trust me on this.