That's very strange. She could have gotten a sore on her neck that made her start scratching it and now it is a lot more than a sore. It probably just hurts so she is scratching it right now. Just make sure to keep an eye on it, especially for infection. Don't forget to keep me updated. :)
We didn't put any treatment in with our chickens till they actually had lice. We use Seven powder and put it in the coop, along with dusting our chickens twice a year.