I don't know what it is about the Fromm's. I wish I did. I see very little difference in ingredients between the Fromm Puppy and the Fromm Adult, and Ava thrived on the puppy food, but not the adult. It's frustrating– I know how you feel, Chealsie. Have you tried the Hill's a/d to try and get a little weight back on Oakley? It's gentle on their system and is higher calorie. It's made for dogs suffering from an illness/trauma or post-surgery. It was a godsend for Spencer when he was sick-- and the chicken breast/brown rice/scrambled eggs that Lisa suggested worked well, too. The scrambled eggs were his fave-- even Egg Beaters which you can microwave in a minute!
I know you're looking for a long-term solution for Oakley, but maybe the a/d or scrambled eggs mixed with kibble would be a good stop-gap? And for some reason, dogs that have issues with grains can have issues with dairy. I have found that with Ava. Yogurt and cheese don't agree with her. Pumpkin has helped her, however, and so has the FortiFlora. She has been on antibiotics almost constantly since I've had her, poor girl.