
Has she seen a vet? It may well be a skin infection or a yeast infection there is no way we could know without seeing it, so first stop the vets. It is best to catch any skin problem as soon as possible and chronic cases can take a lot to get on top of, so to the vet as soon as you notice something wrong.
EDIT - I sound a bit sharp, did not mean to but you are trying to treat the smell not the cause and you need to know the cause and the vet is they best person to see but even vets can struggle to get to the bottom of skin problems so the sooner you start the better chance of success.