Loosing Feathers Around Neck

I noticed recently that one of our Plymouth Rocks (Zelda) is loosing feathers around her neck. At first I thought it was because she was probably going through a molting phaze, but I come to realize that none of the others are having the same problem. She is about a year old to date along with the others she came with.
One of our white leghorns (Sunshine; who is 9 years old) has a huge bald spot on her neck as well (she was feisty, so I couldn't get a picture of her.)

I'm beginning to think it's a lice problem, but I didn't see any bugs on both of them. Zelda, though, where she is bald the patch of skin looks a bit yellowish in color and almost looks dry instead of a normal pinkish tint - it almost looks like she has eczema. Sunshine doesn't have the yellowish tint and it doesn't look dry. I'm not sure if both of them have the same problem, but I'd be surprised if they were.

I hope you bird experts might be able to know what's happening to poor ol' Zelda. Here are some pics. I apologies for the quality of the pictures. Zelda didn't like her pictures being taken. (And getting a close up on the bald spots made the images go blurry.)