One thing you have to think about is that the weaker ones are some times kept away from the food by the stronger ones. When I have to leave for a couple days, I'll leave food and water in the coop as well as out in the run where it normally is. Maybe yours is getting picked on too much and...
BTW, I have one in a delicate state that I started feeding soft bread because she wasn't thriving (peritonitis). Now I'm feeding egg yolk like you, left over cooked green beans (she likes canned), chopped grapes, broken up fries, bits of lettuce, tomato, anything she'll like and preferrably...