It could also be something in his back causing pain, if he's doing it mainly around turns. I once had a gelding brought to me for training that did this in one direction, but not the other, and turned out he had a pinched nerve in his back that hurt when he bent a certain way, we assume because he had twisted it funny kicking the wall in his stall. A chiro and a little rest sorted him right out. I'd have the vet check him for back pain the next time she's out.
"Keep a leg on each side and your mind in the middle"