Do you know it is just one hen with the problem, or are you just seeing occasional runny poops and assuming it is a single bird?
If the later is the case, look up cecal poop on this site. If it is a single bird for sure, get a fecal done and you will know if she has an unusual # of parasites that might cause diarrhea. If it is a single bird that is free ranging, she may be eating something different than the others (cat food, garden scraps, fruit ect) that can cause different feces. Confining her with only layer pellet will solve that problem.
Speaking of food- what are you feeding, and did you recently introduce them to a new area?
I know it is one hen because the poop tray under the roost has mostly normal droppinngs. The butt end of all the hens are clean except for this one. I have seen her expelling this mess.
They have not been moved to a new area. I did recently put up a pen and they are getting out of the hen house regularly.
They were mostly inside all winter with a rare couple hours of free range in the afternoon.
I feed layer pellets. The pellets are always available in a hanging feeder. Recently I have added oyster shell. They get scratch grain maybe once a week.
I clean the poop tray every other day.
The chicks roost on top of the overturned ferret cage. The plastic tray over the nesting boxes (pet carriers) catches the poop keeping the top of the boxes clean. This allows me to easily remove the poop under the roost where most of the poo is located.