I would not personally trust just ONE vet's analysis, especially unless the vet had SEEN the horse working (limping) not just an unmounted exam. Many vets are no great shakes at eyeball detection of lameness anyhow, and maybe the horse DOESN'T do anything when unmounted, that has nothing to do with whether she might be sore when ridden.
Also, my experience is that a fairly large number of horses move unevenly under saddle for reasons wholly or in large part related to poorly fitting tack, chiropractic type problems, and poor riding. My experience is also, unfortunately, that the great majority of saddle fitters, vets, and many trainers too cannot SEE this
Be real, real critical in scrutinizing saddle fit. Remember that the *horse* gets the last vote in whether something's comfy or not - but if you see dry spots or feel areas that bind, chances are pretty good that the saddle is at least part of the problem.
Then, when you are riding the horse, work on getting her STRAIGHT, and strengthening and stretching and suppling both sides. Some horses that are uneven under saddle are simply flopping along stiffly and crookedly, and if you put enough work into stretching/suppling/balancing them they even up.
Finally, though, consider that if she IS faking it -- and I do not believe this happens very often at all, but it does happen sometimes -- WHY would she be faking it. Answer: because she does not enjoy her work. Solution: find work she enjoys more. Really truly.
Good luck,
Pat