I have a hen that is about 3 years old. For the last week, she has shown weakness on her right side, she's got her feathers all fluffed out and appears to not be able to turn her neck to the left, only to the right. She loses her balance on her right side and appears to have limit use of her right leg. She shows no sign of injury other than this sudden issue. When I let the other chickens out to free roam, she does go out with them but continues to have this weakness on that side. Any ideas what's going on?