Chickens do molt at this time of year, and they usually replace all or most of their feathers. They typically start with the head and neck, then the breast and back, then bum and legs. The flight feathers go somewhere in the middle there. If your girl is molting, you should see tiny new pin feathers coming in (they look a bit like small porcupine quills). If you aren't seeing any new feather growth, I can think of a couple of things that might be going on: first, bird feathers grow in tracts - longitudinal lines along the body, rather than all over as fur does in mammals. So if you part the feathers, you can see bare patches sometimes (if the bird isn't very fluffy). Also, layers pull feathers out of their centerline (breast and belly) to create a brood patch. Even birds that don't go broody will have a small patch, although I'm guessing broody ladies continue the plucking process and have a much more substantial bare patch than layers who aren't inclined to brood. It's possible that what you're seeing is just a brood patch or the space between feather tracts, but my bet is on molt.
