I want her to eat again because she's better and you need food to survive in most cases.Why would you focus on getting her to eat grain?
Are you feeding all your birds a complete chicken feed formulated for their age as their primary (90%+) ration?
How old are your birds.
I feed her and the other chickens treats every day. Probably more than I should.Yes, one needs food to survive but grain will only be 10% or less protein as opposed to most feeds that range from 15-22%. If you want her to gain muscle, she will need amino acids. If you want her to gain fat, feed grain.
"Perfectly healthy food" doesn't tell me the protein % nor if you are supplementing the feed with treats.
Dates and mushrooms are perfectly healthy but are devoid of protein and aren't a complete ration. As healthy as they are, I couldn't live long on them alone.