You've seen her often enough already right?
Aside from practicing with other girls... why not just kiss her outright next time you see her? The minute you walk up to her, frame her face a little and just kiss her. Am sure she'd be a little surprised but you'd sense how lingering you can get with her if she starts responding. And then break and just say casually, "Always wanted to do that." and go do the thing that you guys were meant to be doing that time.
After that, you shouldn't have problems kissing her wherever, whenever.