Posting for a friend.....this will be a little lengthy.

My friend's 8 year old mare is acting very strange suddenly. To give a backstory - she has owned this mare since her 3 year old year. She broke her and started her on barrels. The mare advanced nicely and slowly. First entered January 2019. They started consistently clocking 2D/3D while being seasoned. They had some initial issues hitting barrels for several months and then fast forward to the mare bleeding on her in July 2020. She started her on Lasix two months later and the first time on it she placed in the 1D at a big show (Sep 2020). She started clocking faster with the lasix but still wasnt working quite right. So she had her vetted and found a bone chip in her fetlock which she injected (Oct 2020). They began clocking consistent 1D/2D for about 3 months. Friend had some life changes and stopped riding for about 5 months. Horses were moved to new location during this period. Injected her fetlock/hocks in April 2021, starting running again in June 2021 and they came back strong after the break. This lasted for about a month and then things started going downhill. In July 2021, they started crashing barrels, clocking 1/2 - 1 second off their previous times, the mare became very anxious, hot headed, lost weight and muscle tone, had dull haircoat, etc. So my friend had her vet checked again by a different vet (Sep 2021) just to be sure no lameness issues were missed - mostly good, a little sore in hocks/stifles so they were injected. Still hitting barrels, just not clocking. Went to a third vet (Dec 2021) who injected her fetlock for maintenance and suggested wedges on back feet due to angles (just to try)...still no improvement.  Mare started getting increasingly agitated and cinchy, even refused the gate in early Feb 2022. Friend was still not happy with her weight or muscle tone despite changing feed, increasing feed/hay intake, and having her on a good exercise routine. So she started thinking it could be ulcers. Decided to start treatment without scoping (as many suggest, she has treated other horses in past) and give the mare a month off.

She is about three weeks into the ulcer treatment and the mare has now developed a horrible attitude. She doesnt want to be caught, flinches and pins her ears when she is touched, and if you go near her stomach/flank area she will try to kick. This mare has never been a fan of grooming or excessive touching but has never had an attitude this bad and has never been dangerous until recently. It seems to have gotten worse with ulcer treatment!

She has an appointment at the vet for her on Friday to be seen. 

I've been doing some of my own research and have come across some possible explanations including PSSM, HYPP, EPM, Lyme Disease, Leaky Gut, Magnesium Deficiency...those are the ones that stand out to me. 

Any thoughts? Ideas? 

Some horses don't tolerate Omeprazole well, in those cases I like Succeed VF, Stride 21 day immune program (same as hind gut program wirh added Vit E and C), I have even had good results in one tough case with Seabuck, 6 oz a day.  They are all different, just have to be willing to try different things, not all at the same time though.

Treating for EPM may help also, I do this along with one of the treatments above.  Injecting cortisone into the joints can lower the immune system enough to need EPM treatment.

I would of course do what your friend is doing and consult with the vet, but if it were my horse I would want to do an EPM treatment maybe even two treatments. With the steriods from the injections and if she is treating for ulcers I think a good clean out would be helpful. Also as someone else said some horses dont respond to the standard ulcer treatment so may have to switch to something different. The horse may be hormonal as well...

Maybe she went a little too fast with her. She broke her at 3 and was hitting the 2D, then hitting the barrels themselves, when she was only about 5. That's pretty fast. Then she started bleeding the next year. Could anxiety about the bleeding cause ulcers? And what about cysts on the overies? Whatever the vet finds, I might think about going back to the beginning and going real slow and easy. Please let us know what happens. 

Is barrel's the only thing she does with this mare, how often does she run her? She kinda sounds like shes burned out. Have your friend get her checked for EMP and it would not hurt to have her Ovaries checked too. 

Thank you all for the responses! At the time of the vet appointment, the mare acted like a perfect angel. (Arent horses great?) The vet scoped her and found evidence of ulcers but they were completely healed. Then she was ultrasounded for any ovary issues and the vet said it looked like she may have experienced a hemorrhagic follicle....new one on me. In short, it's a follicle that keeps growing and fills with blood instead of ovulating. Apparently it can be super painful and can cause mares to be pretty rude. So with that being the only possible issue, my friend started her on Regumate. I was a little surprised they didnt want to do bloodwork or anything but I didn't go to vet school lol. We are optimistic that it will help!

Have they x-rayed her back?