First, make sure there isn’t a medical reason. Decrease in appetite, refusal to eat, just as changes in behavior, can be red flags that something may be wrong. Time to see the veterinarian (imo).
Otherwise, I would consider a higher quality food, I like Nutrisca (for my allergy girl), Wysong for my senior. I have also used Wellness Simple. My neighbor likes Fromm for her picky eater. Maybe add a little water or homemade plain chicken broth to her food. Mix in a spoonful of canned or a bite of chicken…
Newman Organics is a reasonably priced quality food, I think.
Or consider homemade with kibble as a base. http://www.homeovet.net/dynamic/php/downloads/dog-c8470f2c75dbe4b683205c3919ee2310/dog_diet_complete.pdf
