I would work with her on transitions all the way around the arena, and especially work on downward transitions going toward the gate. If you try to do a downward transition, or slow her and she doesn't listen to you, halt and back her up a few steps, then continue working. Start slow with just walking. Take her up to a good working walk, then when you approach the gate bring her back down to a slower walk. Once she is listening to you and doing good at that, try it at the trot. Make her trot and then as you approach the gate bring her down to a walk, gradually working your way up to cantering, etc. It might take a few rides to get to working at the canter but the time is worth it. I did this exercise with my mare because she was rushing fences and it helped. Good luck.