Have your farrier and or vet check her feet and back for soreness or not being balanced. Also check to make sure your saddle fits well, and that her teeth are good and don't need floating.
After that, if she is still clumsy, teach her to pick up her feet. I have a stocky horse that is definitely NOT clumsy. I do not know of any horse that is clumsy regardless of whether they are stocky or not who is healthy.
To train them to pick up their feet, put poles down on the ground and walk, then lunge them over the poles. Make sure the poles are not anchored... Just lay them down with enough space in between for her entire body. Once she can walk over them, lunge her over them, at a walk, then trot, then if the space is large enough, lope her over them. At this point, move the poles closer together so she is stepping over maybe 2 at a time. Then, get things like a jolly ball, old bucket (plastic,) old dirt bike tire, whatever you can think of and have her lunge on over and around them.
This teaches them not only to pick up their feet, but also to watch where their feet are going / what is in front of them... And it helps to de-sensitize them to thinks like horse eating buckets...
Hope this helps. Connie