We have a four month old Buff Orpington pullet who, until recently, appeared quite healthy. About 2 weeks ago, her feathers started to become puffed out and she developed what looked like a goiter under her chin. However, a few days ago, she lost her ability to stand and walk. When I pick her up, her legs just flop down. I've attached a picture of her in her unfortunate state. Any idea what's wrong and what we can do to help her?