Is there anyplace that she may have gotten her neck caught and she injured it?
Anything rotten or decomposing that she could have eaten?
When was the last time she laid an egg?
It's hard to know what's going on with her - it could be something like Wry Neck which is a neurological disorder from head injury/trauma, vitamin/nutritional deficiency or certain diseases like Marek's, Newcastle and Avian Lymphoid Leukosis.
You may want to treat her as if it's vitamin deficiency - offer poultry vitamins that contain Vitamins E and B. Selenium helps with the uptake of Vitamin E, so give some chopped egg or tuna along with her normal feed.
Let us know how she is doing.