Pomeranian has hair loss on her back

Hello, I have a two year old, female pomeranian, who has hair loss on her back. I believe it's from fleas, though she doesn't have a flea infestation. She's had hair loss in the past in the same area, that cleared up when I started to feed her better quality food. The hair loss is near her lower back. Her hair has a little odor to it, which she also had in the past.

My dog is a very picky eater, and only likes wet food. I'm thinking of trying her on dry food again. I'm thinking of trying brewers yeast to help control fleas. Has anyone had any luck using brewers yeast?