At 3 weeks a head injury or vitamin deficiency is usually the case. In older birds, Mareks sometimes can cause wry neck. Some birds for unknown reasons may have neurological issues. Silkies tend to have problems more often. I would add some b vitamins for the thiamine, since deficiency can cause wry neck too. Egg is good for the small amount of selenium that is needed for vitamin E uptake—too much may be harmful. They may need to be separated if being targeted by the other chicks, and they may need help getting enough to eat and drink. Let us know how she gets along.