I had the same problem
Race horses are taught to more forward without leg, only whip and reins, very hard to break but can be done.
I would go back to basics (if possible her re-trained by a pro.)
90% of the time the race trainer doesnt take the time to break them in properly, and dont realise that if they did they would get a better result they just through the saddle on for a day, hop on the next.
not what you want.
As for collection this is going to take time, i would worry about the little things like bending to the left and right, practice circles, spirils, and work on flexing you may find that she has perfect flex to one side depending on which way they raced her around the track.
after she is flexing and bending you want to get her moving forward before traning her to collect, you wont be able to get collection unless she is forward in her movements
i'm still working on my TB she still turns like a bus going left but not to worried about it yet we are doing lots of work
jac