Well, the main thing that is stumping me is that when she is out in the field, she is just fine. Her frogs are good and firm, although not brittle. She stands fine in the field, and walks fine in sand on turf, and on gravel.
However, I'd like to add, because this may be important, that in the field she is living in quite a bit of mud that goes up to her fetlocks. I have been very careful all winter about thrush, but she hasn't gotten it, and I always clean her feet out before and after a ride, and we usually go through deep puddles anyway.
The mud isn't all over the pasture, but in the area where she walks a lot, to get grain/hay. The main thing that I have noticed is that she tends to put more weight on the inside of her feet.
The only thing that I thought that might have been an error on the part of the farrier would be that I asked him to check for bruising on her hind legs one of the first times I got her, and he said that he found one on her right hind just inside of the white line(unfortunately he told me this after he put the shoe on).
That may have aggravated her feet, and since then she has not wanted anyone banging on her feet.
I have some pictures of her feet, but I'll get some more tomorrow, and I'll call the vet, so that he can come out in a week or two, depending on his schedule. I want to pinpoint what this is all about.
Also, I have known this for a while, but her heels are slightly low, and her feet were trimmed slightly asymmetrically. I'll get some more pictures tomorrow, to see if anyone can see anything.
Thanks for the advice so far!