Unless your pup has exocrine pancreatic insufficiency (highly unlikely), then it is almost certainly a behavior issue. It tastes good to her. Doesn't mean she is lacking anything.
Cheap food just seems to make them happy. The fat source appeals to them. Must smell good. Ellie eats homecooked and she still loves a mouthful of Purina.
It's different to her and she thinks it's a treat or something. I crave food with corn products too. lol.