Gem was always bad with picking up his feet. We knew he had abcesses and surgery, and thought that it tramatized him that he didn't want to pick his feet up.
We would muscle with him to hold his front feet up. It may have not been the best thing to do, but we would manage to pick them out.
Then when we found out he had arthritis in his hocks and right knee, we figured he didn't want to pick up his feet due to that. After getting his feet trimmed, and x rays of his hooves, he's been better, though he does have quite a bit of arthritis between his coffin bone and p2
What i'm trying to get at, is there is a reason why she's putting up a fight to have her feet picked up. It could be anything from a trust issue, like Sonny said, or to a medical reason.
You said she's jumped before, and shown before you owned her. How old was she when she was jumping (before you got her) and how high?
5 years is young for anything to happen, but i personally know a 5 year old horse that has foundered, so you may be looking into a medical issue.
If she doesn't get better, i'd ask the vet to take some x-rays.
Oh, btw, before we moved Gem or even got the vet out, he never showed that he was lame or not bearing weight on any of his feet.