I have had the same problem! But my chicken had more poop on her feathers since she has a lot of feathers. Try wiping it off with warm water, but make sure to not touch the chicken's skin. If it is stuck, use tweezers of scissors to try to remove the poop. Hope this helps!:)
Hope the hen is ok! When my chickens get injured, I clean them up with a wet paper towel, give them something to eat, and leave them alone. Chickens are pretty strong, so they'll get back up on their feet fast!