Have someone hold her, spread one wing and cut the primary flight feathers. Google "how to trim a chicken's wings", there are lots of pictures that show which ones to clip and several YouTube videos illustrating how its done. When I've done it in the past, I've only done one wing. The idea is that when that start flapping, it'll throw them off balance.
Just a fair warning though, clipping her wings may not stop her. I've had some that stayed put after, and I've had others that just flapped harder and got out anyway, whether I cut one wing or both. It may also make her more susceptible to predators if you free range. If you keep them in a run all the time, she'll be safe (unless she still manages to find her way out).
Good luck!
