Sick Chicken - This, too, shall pass?

The same chicken is sick again.  She's lethargic, has weak eyes, and a ball of hardened poop about the size of a golf ball stuck to the feathers of her rear-end.  Not a happy chicken!  I cleaned her up best I could with a wash cloth and warm water.  I couldn't avoid removing some feathers from below the vent... the poo was as hard as conrete!  Upon inspection, though, the vent area didn't look inflamed and there was no discharge.  No discharge from her eyes, either.  Her breathing seems normal.  I hope she's simply constipated, but I separated her from the rest of the flock as a precaution.