I've been working with an ottb mare for some time now. She's very smart and is learning how to be a ridden horse very quickly. She has a lovely canter to the right. She's learned to pick up the right lead and bends perfectly. She's even pretty calm. But when we go to the left, it's like she's on a racetrack again. She'll pick up the lead, but that's the only good thing she does at the moment. She blows around there like she has a bat under her tail and forget about bending, I can't even keep her straight. She puts her towards the rail and her butt to the inside and canters around on a 45 degree angle. She never did this before, this is more recent.
My question is, how do I straighten her out? If I take her in circles she'll straighten out. But as soon as I take her back on the rail she goes back to cantering sideways. This is the only issue she has that's preventing me from trying her in an english saddle. Can anybody help me?