Ok, I realized that I made a mistake. the horse stands like that when trying to take weight off the hind. I didn't mean to imply that Cheyenne is lame or anything. She looks really , really nice for her age, or just for any horse, for that matter. I did notice that her hind hooves are really low and under run at the heels.
My friend has a chestnut Qh who stands just like that and it turned out that the angle of his feet were causeing soreness in his legs, which really ended up making his back sore, too. So, for about a year they put very slight wedged pads on his back feet, and trimmed little by little to change the angle to give him some more hoof under the heel bulbs. I am sure I am not describing it very well. But, it improved his comfort quite a lot. He doesn't need the wedges now at all.