It sounds like she is on a good food UNLESS she is allergic to rabbit/duck/potato. It's not common but it does happen.
I would get her started as soon as you can on frontline. Some dogs have major allergies to fleas. Even if you don't see fleas on your pet, it only takes ONE to get the cycle started in these pets. Then it can take forever to clear up after that one bite.
Your vet can perform allergy testing to definitively tell you what she is allergic to. It's pretty simple but it can be costly. But in comparison to what you are paying now to treat the symptoms, it might be worth it.