Can you post a picture of the hen, so we can see how she's standing? Also her vent area.
Do you known when she last laid? Holding the tail down is often a sign they are not feeling well. Are her droppings runny? Is she eating, drinking? Does she have access to both grit and oystershell all the time? Check her over for any injuries or wounds hiding in feathers. Look for signs of lice/mites. Feel her crop, see if it's empty, full, soft, squishy, hard, etc. Check again first thing in the morning before she has access to food or water, see if it's empty then (It should be, then). Look for any signs of discharge from eyes, nares, beak, any facial swelling, any coughing, sneezing, wheezing. Look in her beak and throat for any plaques or lesions. Have you ever wormed your birds or had a fecal test done to check for them? You can clean the droppings off with a wet washcloth. If the droppings are dried you may have to let them soak a little to soften up. Until you know if she's sick or not, I wouldn't give her a bath. Also, check her for any signs of molt, any pin feathers coming in anywhere, under wings, around head and face, around vent are common starting places.
