Mrs. AK-Bird-Brain :
Have you checked them for lice? Sometimes that can cause them to stop laying. Is she fully feathered, or is she missing some feathers at the base of her tail? Check around her vent to see if you see anything.
If she's an internal layer, sometimes you can feel her abdomen and if you feel something that feels like an egg in there, then you know. I had one hen that had stopped laying for months, and it felt like there was an egg right there... it wasn't. When we finally culled her, there was a mass that looked like a very large baking potato in her abdomen... all the eggs that had smooshed together.
I hope she's not an internal layer. Is it possible she's hiding them somewhere?
Now, I did consider this, or fleas, because my mom's dog (next door) had fleas. I also have one pullet that has a bare back now because they have been picking at her. I did notice that Nutmeg is missing a few feathers, too. Not right back by her tail, but more in the area that the roo mounts her. He does not have spurs yet.
I checked several of my chickens and found that they are so clean!! No bugs in their feathers! I will check again, though. I would think, though that if she has lice, they all have lice and it would affect all their laying. My dog is clean, too, btw.
I would like to feel her abdomen, but I don't know what to feel for. Do I feel back by her vent? I did pick her up the other day and didn't feel anything unusual. I will be doing a thorough check on her tonight. If I can catch her this afternoon, even better.