Not Laying and Poopy Butt

I also posted this in diseases.

I have an amerucana (1yr) that has stopped laying a couple of months ago. She was molting, so I didn't worry much about it. Since then other hens have molted, stopped laying and started again, but not her. Just yesterday I noticed that her butt feathers are collecting poop. This happened to another hen, and I cleaned her off and no problem, but with this one I am worried since she is still not laying. All my hens get apple cider vinegar in their water along with a vitamin/electrolyte. I also give them black oiled sunflower seeds each morning as a special treat. They free range during the day, but I have locked her up for a few days at a time to make sure she isn't hiding eggs and nothing. Here are my questions:

Is the messy butt indicative of a problem? What is the best/easiest way to clean it?

Any ideas on the laying? It has been at least 3 months and we miss our pretty blue eggs.

Thanks - Shannon