This horse is not cow hocked. Her hind legs are actually straight. When a horse has its hind toes pointed straight forward the horse is actually bow legged behind.
The hind leg is actually a spiral. It is built this way so that the stifle will clear the belly and because a sprial works like a powerful spring. It is really physics. Read the books by Deb Benett Phd.
Conformation show breeders breed for toes straight ahead behind and horses with this conformation win in the QH halter class. It is one of many reasons why Halter conformation QH's do not ride.
Here is an image of Cow Hocks. This mare is straight behind with a normal spiral. She should work well under saddle and be able to push off and use that quarter horse rump musculature