If she is broody (sounds likely), then she will want to stuff her crop really full once or twice a day, so she gets enough food without being off the nest for long.Okay yes hopefully her crop is just full from food, I wish I had known sooner so I could compare it to how it normally is! Because her sisters is like almost unnoticeable in comparison so now im like did that one not get enough food??
A non-broody hen will eat smaller amounts all day long. She doesn't have much else to do--eat, preen, take a dustbath, eat some more. But the broody hen needs to spend her time on the nest, so she rushes through the eating and mostly skips the rest.