One of my RSL hens has a dirty but area, like diarrhea dripping down her feathers. Also, the area below the vent appears to be swollen. She eats and drinks and runs around with the others as usual. The only thing i notice is she is always last to get off the roost in the morning, the others run out as soon as i open the door, but she will stay behind for 5 or 10 min, other than that, acts normal. Any ideas? Thanks.