We bought our OTTB when he was 5 and had been off the track for less than 3 months.
Those were tense and dangerous days.
As a mom, watching her son working with this horse, those were the scariest days of my life.
He was calm and agreeable, MOST of the time....but when he didn't get his own way, he flipped out in a major way. He would whirl, kick, and rear in my son's face, striking out with those front hooves at times so close my son said he could feel the wind on his cheek.....
I would say it took AT LEAST a year of constant, as in every single day, of groundwork before he was deemed safe enough for anyone other than my son to be around. He had major biting issues, severe food aggression, and an attitude that HE was God.... These issues took time to resolve.....as for the lunge whip, we also had MAJOR problems with that. Pull out a crop or whip and he was in FIGHT mode.... as for the groundwork, he would bite or kick at the carrot stick.....
Under saddle, he was great in an indoor arena, very aggreeable but very forward...,outdoors he is a loose cannon.....he wants to GO GO GO.....he is very hard to bring back down and to KEEP him down....in his mind, outdoors means gallop.
At least your mare doesn't have so many issues it seems....so count yourself lucky.
My only advice to you is to start from the ground up....make sure your horse understands that YOU are God, not her.....which translates to complete control, even with the lunge whip, on the ground.
What we have found with our OTTB, even NOW two years later at age almost 7, if you give him an inch, he'll take a mile.....rules and boundaries must be clear and firmly established. They are not negotiable. If you negotiate the rules with our OTTB, you WILL wish you hadn't.
At this point in time, he is a perfect angel. You could not ask for a more agreeable and well behaved horse. His biting has ended, due to us working extensively on this for over a year, he does not whirl, rear or kick out at humans anymore....he does still have food aggression with other horses, but NOT with humans.....so that is still a work in progress.