Supplements are a risk too.It's best to just stick with the highest quality diet that provides appropriate vitamins and minerals,rather than having to add more.Pelleted foods aren't great for any species though,so you'd need a very good mix instead(Burgess dwarf being best,so take some time and figure out a way to get that as it would have everything necessary and provide appropriate nutrition).
Veterinarians can be a bit unreliable sometimes when it comes to nutritional advice and general care
It's very unfortunate,but their education focuses on medical rather than nutritional so you can't exactly expect them to be nutrition experts by any means!
I'd definitely work on getting her onto a better food that is truly species appropriate(one that actually allows foraging behavior which is essential),and determining if this loose jaw situation really affects her in any way rather than assuming it's a definite problem(which it might not be,or it could be entirely unrelated to an inadequate diet!).