How old is your girl?? From all the descriptions I would guess she is just slowly on her way out. Does she look old? I've had some die of old age and some were similar to yours. They wouldn't/couldn't get up on the roost at night so I made a space in the corner on the floor. I could see in their eyes that they were aging. They would still go out and eat with the rest of the girls to the day they died but like people who get old, did so more slowly. They stuck closer to or in the barn rather than going out to forage.