I agree with Thenrie. You have her in a round pen already, start from there.
I would start first by asking for forward movement. Don't expect a full cirlce around the pen at first. Start with small steps. Ask for her to move off (either with a whip, or lead rope), once you get a few steps stop asking and back up a bit. Repeat until you get her moving forward consistently. Once she is relaxed about moving around the pen when you ask, start having her change direction. At this point she will have realized that you are in control.
Next I would start asking for her attention. Lets say she is ignoring you as you climb into the pen. Kiss, slap the rope on your leg, jump up and down what ever it takes until she looks at you. If she completely zones you out, make her move. Not a slow dinky walk, but a brisk trot. Back off after a lap or two. Once she has stopped ask for her attention again. If you get her attention, then start moving around. Go to her left, then her right. Make her move around to keep her eyes on you. If she looks away, make her move off again. Eventually she will understand you want her attention. This is a great time to bring in the treats! Slowly circle her, going from side to side and getting closer each time. If you think she is going to shy away, don't push it, back up a bit. At some point you are going to end up close enough to touch her. I would only touch areas she is okay with at this point. Only pet her for a few seconds and then walk away. Make each time you pet her a bit longer. If she runs off while you are petting her, don't let her stop on her own, make her move a bit, change directions, you want being away from you to be work.
I would keep going at this until you can touch about anywhere. Desensitizing the face first would be best. Then you can get a halter on and control whether or not she can run off a bit more.
I hope that was mildy helpful!