Why is my hen skinny

[henplusrooster]

I have a black australorp hen and she is kinda skinny. My other black australorp is big. But my hen is skinny and her poop is sometimes runny and chunky. Is there something wrong or is she just different from my other chickens.

 

[sbhkma]

How old is she? What is her appetite like? Is she eating and drinking? What's her crop feel like-empty, hard, squishy? What does her comb look like - red, pale, bumps, etc. Is she walking ok? Is she laying? Have you looked for parasites around her vent and under wings? Has she ever been dewormed?