Chloe is molting. Even though she's the youngest chicken (about 18 months old, which is prime molting time), the older two have managed to escape a full-blown feather explosion like she's experiencing. I wish I could get some better pictures for you, but suffice it to say, she looks an absolute mess.
Here you can somewhat see her neck. It looks like it's been through the wringer:
And, here you can see her missing feathers. Paco has been enjoying them as a backyard snack:
She's stopped producing eggs during this whole procedure, although I think she's still spending a bunch of time up in the nesting box. Poor girl.