Have you ruled out coccidiosis, which can cause a failure to thrive? She looks hunched or puffed up like many pictures of it. Instead of bringing her inside, I would leave her with her flock, but in a cage with her own food and water. Bring her outside in the shade with them during the day where she will enjoy their company without being harmed. Symptoms of coccidiosis are lethargy, hunching, poor appetite, and runny droppings with mucus or blood. Corid is the treatment. Does she move her neck normally, up and around? There are skeletal deformities that can cause spinal abnormalities.