Behavior tells us more than the appearance of poop, but taken with her lethargic behavior, your hen is feeling sick.
That said, it's anyone's guess as to why she's sick. You will need to do some checking and sleuthing. First, check her crop. Full, empty? Soft and spongy or hard and over-full? Check it tomorrow morning before she eats or drinks to determine health of the crop. If it's not perfectly flat and empty, Houston, we have a problem.
It could be she has an egg stuck. Is she holding her tail low and flat and pumping it? Has she ever laid two eggs in one 25 hour cycle? Any soft eggs recently? How old is she and how long has she been laying, if at all?
Has she been free ranging where spoiled veggies or fruit have been rotting?
Any insecticide use in her range area? How about machinery leaking fluids onto the soil?
The vet will be able to help you more if you have answers to these questions.