Different ways to look at it.

If you want to save some money, then gradually change her food to a low carb wet food over the next week and see if that helps. Avoid fish flavors as they can cause problems in some cats. Try to go for rabbit or chicken flavors.

On the other hand, if it is something thats wrong, that your present vet has missed, will you be angry at yourself for waiting before you saw a new vet.

Personnally I would try the new diet and see how it goes, as the stress of a visit to the vet isnt good either.