I would have someone look into her mouth. Often a piece of vegetation can get stuck somewhere in the mouth and cause irritation or a sore. It will be a good time to see if her teeth need work too.
No, I don't think you've "ruined" her training. When a horse suddenly starts reacting like your horse did I always suspect pain somewhere.
Plus, this spring a lot of the horses seem more hyper-reactive than usual. You may have run into a perfect storm of spring fever, a sore in her mouth, and possibly a spring heat cycle which can be worse than all the other heat cycles combined. Plus the spring grass is coming in and she may need to have her grain ration cut down drastically at least for a month or so. If she is not on grain I would severely limit her grazing, spring grass can be like rocket fuel.
Get someone to look into her mouth.
Try something different. You must reward correct behavior! Teach them to lower their head with a treat in your hand. My horses always know there will be a small treat when the bit is in their mouth. You can try putting a bit of molasses on the bit itself before every bridling.
I agree with all suggestions so far. Don't panic. My guy did the giraffe routine, acted stupid about saddling, cinchy, sidestepped when I tried to mount. he had a whole bag full of tricks when I got him, plus he could put on a very convincing dramatic showing of spooks and spins. I just kept chipping away at it, and tried to get some miles on him, because he's much better with regular rides. Totally agree about getting them off fresh grass, teeth checked, even if you use bitless (which I do). He came with a bit, but I tested him out bitless, and he was actually a wee bit better, but still lots of tricks to iron out, but putting on the bridle wasn't one of them. I used to say every horse had a trick, but some horses have more than one trick. The main thing is if they do pull some stunt (and you have checked that it is not due to pain), to just persistently keep working on each issue, slowly. He still tests me in little ways, but he just knows I am going to keep insisting until he does what I have asked. Each spring there is a bit of regression with fresh grass, or wind, or maybe it's cosmic rays.
Here is my personnal advice. You should try a bitless bridle, even you ride her or not with it...then reintroduce the bit gently...even try an apple in a bucket trick...caress the top of her head behind the ears, take it gently easy...
The other day I really tricked my mare who wasn't taking the bit for 2 months...I put her bitless bridle on...then she thought 'OK, I got it on'...then I put the bit bridle on ...on top of it and she didn't move ! No giraffe stuff...she was just so suprised...(what? two times in a row ?!, 2 bridles on?) ...then I left her like that for a few minutes then I removed the bitless underneath ! We had a great gentle ride with the bit, she now takes it again...I have no idea what went into her mind which was creating this refusal...I had to change bridle too...which was used to be her bit bridle is switched with my gelding, she likes his better (same bit...just different leather on the bridle...don't ask me...?!). So I would recommend to try a few things. The honey on the bit didn't make any difference to her, she was refusing it...it was about the action to get it over her head and touching her mouth with my fingers...as soon as she could ear the metal (as for the bit) she would do her Giraffe again...
Her teeth are fine, she is all good. She has no pain.
Just sometimes, you never know what is going on that is so so wrong ...with patience and new tricks, they will accept things a bit differently then before and then it is all good again, no big deal. That is my experience. Good luck !
My mare was a school horse in her past and she always had a shy mouth (I have hard time to deworm her for example), I believe she has bad old memory of riders jerking with the bit in her mouth. That is why I rode her bitless so much...then it is a little tricky to introduce the bit again, but I still do, so she can take both.
Remember horse don't worry about the future of the past, she lives the present moment...but they have amazing memory. I don't think all your training with her is a waste, it is never a waste !
Hope some of those tricks can help you !
Good luck !
I spent two years training an ornery 18 year old mare, who used to be a hunting horse and hadn't been really ridden in years. First three weeks I couldn't even get on because she wouldn't let me put her bridle on. I spent a lot of time in the stall with her. I would tack her up in her stall, then when the bridle came, I would attempt to put it on. If she tossed her head I would sit down on the ground in the stall. Eventually she would lower her head and sniff me, I kept repeating this until she would take it, then give her a treat and some love. It took a couple weeks but she got more trusting of me and now she takes the bit no problem!!
It's been many years since I had to use a bit.
I learn a lot in this source.... Hors is very friendly animal.
I would get your trainer to help you put her bridle on and see if it makes a difference. Horses learn through conditioning so you may have inadvertently reinforced this behaviour. By jerking her head away from you, she is learning that this is a good way to get out of having a bit put in her mouth because it sounds like she has been successful. If she does have a real genuine issue with the bit and there are no underlying causes, like her teeth are bothering her, then I would get her used to her mouth being handled. Stick your finger in, get her used to opening her mouth for you and as soon as she does, give her a little treat and repeat several hundred times until she associates it with a reward. Progress on to putting the bit in or just having her head handled as if you were going to put the bit in. I use a lot of advance and retreat tactics with horses that don't like certain things done. You want to retreat before they do so that they think it was your idea not theirs.
A thicker bit can often be more irritating btw. It depends on the size of the horse's mouth as to what bit you need. But in your horse's case, the bit is not the problem because it didn't even go into her mouth!
And biting you is not allowed! That behaviour should get a very clear consequence! And don't pretend, all of you, that you don't ever smack, tap, hit your horses! I'm not saying go crazy and beat your horse with a two-by-four. But come on, what would a more dominant horse do if an underling came along and tried to bite it? It's going to either attack or retreat. But it's not going to sit there and get bitten.
So what exactly would you do if a horse tried to bite you when your putting it's (bitless) bridle on? Just curious. Have you never observed horses in a group setting? There is no question there's a pecking order. And anyway, I'm not talking about dominance and submission. I'm talking about classical conditioning. Using positive or negative stimulus to reinforce a desired behaviour.