Maybe some of my experiences will give you the courage you need to ask this girl out. There are a few that I want to share with you:
A. I had been friends with girl A for a couple years. We were both at the same party, dancing together when I told her either that I loved her or that I liked more than as a friend. I don't remember exactly what I said. She did not like me as much as I liked her, and was a bit overwhelmed. She excused herself, went to the bathroom with her best friend, girl B, and shared it all with her. Girl A and I saw each other all the time as a normal part of our separate lives. It was awkward for a while, but since we were always around each other, we just kept talking to each other and worked through it. We remained friends.
B. Girl B, girl A's friend, was also my good friend. A year or two after the girl A incident, I believed I was in love with girl B. This time I just asked her if she wanted to go out with me on the weekend. I can't remember exactly where we went, but I just kept it relaxed and we had a great time. We went out a couple more times and the romance just did not blossom like I originally thought, so we remained friends and started going on double dates with people we were more romantically interested in. We are still on good terms.
C. I had actually known Girl C for longer than either girl A or B. We met again at a party after a long time of not being around each other. In our conversation at the party, she offered me her phone number and address. I told her flat out in front of some friends that I had no intention of calling her or visiting her. I said I had no interest in dating her. I also told her that I liked her fine as friend and she could count on me if she needed a ride somewhere or some help with something. It sounds harsh, but it took her all of 10 minutes accept that. We actually became good friends, did all kinds of things together, and had a lot of fun. We are still on good terms.
D. Girl D was also friends with girls A and B. They were a bit of a trio. I was friends with all of them. At some point, I asked girl C if she wanted to go on a date with me. I had previously obtained her father's permission to date her (we were still in high school), so when she said she had to ask her parents and she told me her dad said no, I chalked it up to her wanting to avoid personally rejecting me. I knew she was not interested in dating me, but I thought maybe she just needed to give me a chance. I asked her a couple more times and she eventually agreed to go out with me. It went nowhere, and we both just moved on to other people. There was no bitterness nor awkwardness. I spent my energies on other people from then on.
E. I met a girl in college. Asked her out to a movie in the park because she was interesting and focused on getting to know her and her sister who tagged along. In a few weeks, I fell in love with her (not the sister) and within a month we were engaged. 8 months later we were married. That was 8 years ago and we have two children now.
The point of these stories is DON'T UNDERVALUE FRIENDSHIP. And don't make this artificial separation between dating and friendship. You SHOULD date your friends. The purpose of dating is to find a spouse, a life-long companion, a life-long best friend.
Take the emotional risk. Just ask her out. Be a good friend and a gentleman. Treat her well and remain friends no matter what happens on the romance side. Also, take the physical stuff slowly. It seems like a lot of people want to start kissing or more right away. If you really like her romantically and you get the feeling she might be feel the same way about you, try holding her hand. If you are wrong, it is easier to recover from. If you are right, it is easy for her to accept and start forming a stronger romantic bond.
Good luck.