Good luck with your mare, sometimes all it takes is a GOOD farrier.
I bought a mare 14 months ago (for endurance of course) and haven't been able to keep her sound for longer than 30 days at a time. We've looked into everything, and yes, we did do a pregnancy exam, and no she's not :). We've had x-rays, ultrasounds, scintographic studies, more x-rays, more ultrasounds, traveled to specialists, etc.
To make a long story short, 3 weeks ago they diagnosed her with founder due to laminitis. 5-8 degree rotation. I was devastated, cried for 2 weeks. Couldn't figure out what could have caused it. She's had the best diet, the best care. Vet said to start thinking about making a very hard decision.
As a last resort, I called a farrier I heard speak at an endurance clinic a year ago, he lives a good ways away, but I asked him if he would please come down and give me a second opinion. It turns out he doesn't believe she even foundered. The first thing he did was look at her x-rays, and proceeded to take 3 hours to trim and balance her. He sees no evidence of laminitis, he believes she has a more upright build on one foot (sort of like a club foot, but not) and just needed to be properly balanced for quite a while. We took more x-rays (a vet happened to be at the barn at the time) and will be able to compare before and after on Tuesday. He put temporary pads on for her ouchyness, and told me to go ride her. WHAT???? You can't believe how happy and relieved I am.
I THOUGHT I was getting good farrier care. My farrier isn't a bad farrier, he's a great guy, thoughtful, gentle with the horses. He just didn't recognize, or know what to do about her little difference. My vet couldn't see it, and the specialists never saw it.
I don't know that we're completely out of the woods yet, but I'm hopeful.
The moral is never be satisfied, keep looking for answers, and ALWAYS get the best farrier you can find.