The first thing I would get checked are her teeth...make sure that she doesn't have any sharp edges on her teeth, no abscessed in her mouth, etc...
Then I would just give her some time off from riding. Not to say riding her is a bad thing, but just let her be a horse for a while, and get her mind off of the whole racing scene, and get her 'settled down' mentally, physically, and emotionally...the life of a race horse is all "high". Give her some time off in the pasture, to just come off of that high. I would even be hestitant to do a whole lot of ground work, except what is necessary to keep her manners under check.
When you do start working her more seriously again, get her to respect the bit on the ground first. Get her to yield to it side to side softly, ground drive her, get her to back on with ground driving, etc...Don't get on her, until she does everything with the bit softly and willingly on the ground, without tossing her head or resisting.
"The ideal horseman has the courage of a lion, the patience of a saint, and the hands of a woman..."