Why does my dog have bad breath...?

...when she is on a grain-free diet? Any ideas why????? She is allergic to everything!!! We used to feed her a rotation diet of Wellness Core, Acana, TOTW, Orijen and Natural Balance (according to how much money we had that month). I've tried Prey Model for several months as well (she only does well on red meat, poultry gives her poops cept for quail). We usually keep her on a food for about 4 months at a time to see if anything improves. She has been to the vet for a full check up. Teeth are great. Stool sample was fine. Vet suggested we check her diet. I just laughed. He said to try putting her on something that has high quality grains in it because her was worried she was having problems with potatoes as the carb. I didn't want to do that because grains are bad, right? She had a skin test and is highly allergic to grass. I live in rural NC. There is a LOT of unavoidable grass here. We got a second opinion from a pet nutritionist because we know how clueless vets can be about pet diets. She was quite shocked that my dogs breath was so bad when we brought her in. She said the same thing the vet told me. When we adopted our dog she had a very bad ear infection and it wouldn't go away (even with antibiotics). The grain-free was supposed to help with this but she maintains an ear infection for 6 months out of a year (yes we clean them daily). We put her on Canidae ALS three nights ago and the bad breath is gone. She poops twice a day now (only once previously). Her ear is getting very bad again. I'm not sure what to do. We keep trading one problem for another. The breath is SOOOO bad that it can't continue. Likewise with the ear infections. I grew up in a house with 8 dogs and have never had any issues to match this one. My vet is out of ideas. Our nutritionist is stumped too. Our girl is a Jack Russell if that makes a difference. Anybody out there have any "useful" ideas?