Thank you so much for your reply everyone, and I would like to give you guys an update. I know when a horse gets themselves into a panic there is no learning to be done, and since their reactive side often overrides the thinking part, you essentially have to wait it out. Which is what I had to deal with this time.
As I mentioned, I rode this mare after we got back home until she started doing a bit better (so we have a big ball in the arena, and her owner said "she's always hated it", which meant that as she got close to it she rears, spins, loses her mind the same way she did on the trail. So my goal for the day was for her to push the ball with her legs several times without arguing. I would wait til she got out of her frenzy, then try again. She figured it out and did what we asked. We quit).
The next two days I worked with her on being away from the herd- I put her in a separate pen, fed facing away from the herd (she didn't eat for a day because she refused to turn away from the direction her friends were in, even though she can only periodically catch a glimpse). I also worked with her on some basics, lungeing, some ground respect. I figured we'd start at the beginning.
Yesterday I got on her in the arena, and we rode. She was great. Gave me one sass when she tried to trot off the second I hit the saddle- but she was corrected quickly and no more problem. Then we went outside with 2 other people. She led, she followed, she stayed between the two and walked beside them. One of the other horses threw a fit but she didn't feed off him at all, she was calm and super responsive, light on the bit. I was SO excited.
So I put her in a stall to get some food and water before I turned her out, everything was good. Then as I went to take her out, a little girl trying to ride needed a bit of help and I just tied *my* mare quickly to a post with a quick release tie to go over and help her. Now a little background information is needed. While working towards my license, I am working with two other trainers that are knowledgeable and certified, one of them trained in Europe. When outside horses come in we talk to and have a questionnaire for the owners to identify what kind of problems the horse is having. The owner told us that this mare (she is a 8 yr old OTTB) has never had any problems tying at all, so we weren't worried. And we use cross ties primarily in the barn, and she's never given us any trouble. But my guess is that she has always used cross ties at home (I know the place) and has never been trained to be tied anywhere else. Because I tied her, and the second I turned my back she pulled back, and just LOST it all over again. Luckily the little girl was in the fenced indoor arena and the only other people there were myself and one of the other trainers. So she threw her head so hard she broke the first halter. So we figured we can't let her learn that she can pull and be free, so she was tied up again and we just waited with her. She would pull, process, pull. And go forth. So when she was processing we tried to go over to her and praise her, but she wouldn't let you near her. She tried to strike and a quick three crops to the chest stopped that, but she wouldn't stop pulling. She yanked so hard she landed herself on her butt and put extra pressure on her face. We made her get up by giving her a tap on the butt for incentive, and she did.
So we weren't trying to meddle per se, and we were trying to let her figure out that standing still wasn't putting any pressure on her and it was really just the simplest way, but we couldn't leave her alone to figure it out either- on the third blowout she yanked on the rope, put some pressure on the halter and tried to lie down and just give up. We had scissors and a knife on hand and immediately cut her lose so she wouldn't choke, and she was fine.
She would come down and process for a few minutes, and then fight again. I don't know WHERE her thinking side was, but nowhere to be seen. Anyway. This lasted for over 4 hours! We were done at 1 am.... Then she stood. Still. And stood some more. And then we gave her a bath and some food.
And so now my next question is...what would you guys have done? I mean at one point I felt it was dangerous to her to continue because she was just trying to lay down and give up, and had we not been prepared with scissors and a knife she would have choked herself. And on the other hand, this was SUPER dangerous behavior and it would be a hazard to any of her future handlers if she was let to get away with this kind of behavior without dealing with it. But I wondered how you pick and choose your battles like that? Like I said, I have had lots of stubborn and green horses and sometimes both, but I've never seen one like this.
The sad thing is, she really is a smart, beautiful mare and she is friendly and goes well under saddle, she has beautiful movement and is responsive to a rider. But it's like somewhere along the way, probably when she was trained at the track or trained afterward, a critical step got missed in her training that led to these kinds of problems. And she has been allowed to get away with this kind of behavior, having led to her owner not being confident around her, and letting her get away with even more behavior.
It makes me so sad :(