The grain could be making her worse... Low grade laminitis can be caused by diets high in grain and sugars. I would take her off the grain. I would feed her alfalfa or alfalfa/timothy hay pellets along with a general vitamin supplement, like Select II. That will give her all the nutrition and calories she needs, and eliminate the risk of laminitis from grain. If you go with a powdered vitamin supplement, just use some water to make it stick to the pellets.
If trimmed properly, a horse should NOT be lame after the trim, even barefoot. She might be tender on rocks, but you should be able to walk, trot, and canter her in soft pasture or the arena, right after she's trimmed. Sounds like you need a second opinion.