I thought about a heating pad, but that would only warm her from the bottom. Would that be enough? When I touched her back, it was so cold before she was brought in. My coop is pretty small--3x4.' If the wind comes out of the south, it can blow right into the open door, and my chickens sleep on the floor. If the wind blows in other directions, the chickens don't get a direct draft.
She's in the parrot room with her Serama buddy, and she's finally moving around, eating and drinking. I'm afraid she might have died had I left her in the coop. I will check out the K and H heating pad, and thank you! I guess a sweater is out of the question. I think she might have gone out in the rain and got damp, and that started her chilling. And having a sweater on would just make that worse. I don't want to worry about her anymore, so I'll keep her in if I have to.
Good for her that you were paying attention! At least she is warm now.
For the future, is there anyway you can close the door to the coop or somehow minimize the wind blowing right into the coop from the south? Chickens hate drafts. Good ventilation is key, though.