I've had one or two nasty experiences with my mare...the culmination of which being an ambulance ride to the ER right in the middle of my mounted police certification and crutches for 2 weeks. That was the last time I was going to let anything even remotely like that happen again.
Mares can be funny. I remember when I bought her, my mom (who's been training horses and riders for over 30 years) said, "I told ya you's crazy for gettin' a mare!" Now, I've been riding for 28 years and have been in all kinds of death-defying (literally) situations, and I've always gotten right back on, but that last one shook me up quite a bit (maybe because it dawned on me that, for once, I might not actually be able to walk away from a hard throw like that if it happened again). I even considered selling my horse and getting a gelding. But then I was on YouTube watching the world class dressage people...riding their....mares...and the horses were behaving wonderfully. I also had a hard time selling because I would look out the window and see my horse, and to me she looked like one right out of a magazine, just like I'd always wanted. I realized that she wasn't a bad horse, she just had a few issues that needed to be addressed.
So, I started researching everything I could about mares and what makes them tick. They really are worlds away from geldings, and the things I learned actually gave me a lot of confidence to try again and "see if this works". I'm glad I didn't give up. Now, 2 years after what we now recall as "the day the lights went out at training", people just can't believe 1.) how great she looks; 2.) how well behaved and responsive she is; and 3.) she's a mare that is as even and well-tempered as any gelding (if not moreso...and without the use of any fancy supplements, etc.)...and the best part is to hear people say "I wish my horse was like that".
Here's what I learned, maybe it'll help distract you from your bad memories a little and help the both of you become a way better team than you ever have been before:
1.) Diet, diet, diet. You can't feed a mare like you feed a gelding, just like a woman can't eat the same way as a man. Of course, what you feed and how much depends on how active she is, but unless you're riding for several hrs/day or going over fence after fence after fence (or anything athletic that consumes huge amounts of the horse's energy) then check your feed. For example, high protein performance feeds may be great for a gelding, but it might be too much for your mare. What a horse (and a person) eats directly impacts the health of the thyroid gland. Females have a significantly more difficult maintaining a healthy thyroid than males do, even in horses. In males, thyroid problems may simply result in decreased sexual appetite, muscle weakness, and lethargy. In females, an over or under active thyroid can cause (deep breath): weight loss, heat intolerance and profuse sweating, frequent bowel movements, changes in appetite, sleep disturbances and tremors, hair loss, fatigue, dry skin and hair, hoarse voice, constipation, heavy periods and mood swings, muscle soreness, muscle weakness, lethargy, depression, trouble w/ concentration, slow heart rate, poor memory, nervousness/irritability, fast/irregular heartbeat, muscle aches, and of course the cherry on top...rapid hormonal fluctuations which leads to irregular monthly biological occurrences. Males don't have the same horemones, nor do they experience them on a monthly cycle like females do. When it comes to biology, you and your mare are both mammals...so you have quite a bit in common in that department. Our diets have everything to do with whether we retain too much water, experience cramping or not, moodiness, discomfort, etc. Your diet effects your thyroid, which is responsible for regulating all of that. Fun stuff, huh! LOL **Note: don't just check your grain-feed. Check your hay and any supplements she gets, too. Alfalfa hay is extremely rich in protein and calcium...but it's a bit much for the average mare to be having more than a flake or two/day (depending on the workout). Supplements bump up your percentages, too, sometimes. ** You can also give her a tbsp of dried cut red raspberry leaves in her feed to help her with the cramping, bloating, etc. and help tone her uterus. It's the stuff that's in Mare Magic, but I just used food-grade stuff from the herb store. It works like Midol, that's all. Doesn't impede performance and it isn't a drug, so it's legal. It's like drinking tea when you don't feel good.
2.) Go over your tack. The equipment that you're using may not be quite suitable for your mare, or maybe she just needs something different. There are so many bits and saddles to choose from. She may find more comfort in something else. Maybe the saddle doesn't sit right on her...all that stuff.
3.) Health. You already said the vet gave her a clean bill of health, but that was for her being safe to ride physically. How is she internally? Does she have ulcers? Do her "piles" look like healthy horse piles? Is her urine overly yellow, cloudy, or smelly? Drink too much? Drink too little? Etc. These are things we sometimes take for granted or that we pass off as being temporary (if we notice them at all). Even though they're not necessarily serious ailments/symptoms, they CAN cause a decrease in performance or even willingness to perform. Your horse can't tell you what's wrong or what hurts, so you have to learn to watch for the signs and fix the problem (not just mask them).
4.) Go back to basics. When my girl threw me, the first thing I did when I was able was to go all the way back to the beginning and start all over...as far back as basic groundwork. Horses have an amazing way of learning/unlearning behavior, and how good a horse turns out when all the training is said and done, is directly related to how solid his groundwork foundation is. Going all the way back to that stage of training also helps the horse focus on refining old skills, which gives the both of you time to forget "what happened". It also helps the horse regain its confidence and helps erase the negative associations from its mind. Since these are basic lessons, your horse will succeed in them by leaps and bounds, which is good for anybody's or anything's self esteem. Go slow. Stay at the same training level for a couple of weeks if you have to. You can still ride, but just do "fun stuff" - trails, play games in the arena with others, walk down the road, etc. Going back also helps the horse remember some things she may have forgotten along the way...things that might have let up to the "shifting hind-quarters" issue that got you here in the first place. I certainly don't remember everything I learned in elementary school, so it's unreasonable to expect your horse to remember every little thing...especially the stuff that hasnt been practiced as much. Something else that I started to incorporate into my horse's training were some "Extras"...like teaching her to use voice commands instead of aids all the time, and even learning to do some simple tricks, working around obstacles - bubbles, balloons, walking over mattresses, tarps, hoola hoops, etc. Horses actually do like to learn, so you can help keep your horse mentally fit and sharp by teaching her something new every so often...doesn't even have to be related to jumping...just anything!
After I took this approach, I wasn't afraid anymore (and I learned a TON about horses that I never learned in my 28 years riding), and now I hear "Man, I wish my horse was like yours." It's nice. ;^)
Didn't mean to write you a book...just trying to offer some hands-on help and encouragement.