If she has a yeast infection, you will need to give her Antibiotics to cure it. I have a yellow lab, Miller, who has chronic ear problems, and if it progresses to the point that it is an actual infection, there is no other way to cure it (that I know of). The key is to not let it get to that point, which requires diligent cleaning.
Also, the root cause of the ear infections must be addressed. It might be food allergies . It might be what you think it is - the wafers - but maybe your dog is allergic to other things you are feeding her. Miller must have been allergic to his dog food, because when I put him on a special prescription diet (for diabetes, actually), his ear problems have almost completely vanished.