A photo would be helpful...white crusty ring....I'm having trouble imagining what you are seeing. Is the ring around the neck like a collar? Or are you talking about a circular ring, like a donut or like a coin?
White could indicate anything from molting dander to possibly feather lice to ringworm (although rarer in a chicken).
It could be mating damage (if you have a rooster), or something else as bizarre as she is putting her head through a fence to eat treats on the other side and creating feather damage around the neck (had one do that acutally).
A photo would help with a bit more info on its occurrence.