I suspect this hen has an egg stuck, perhaps is in the process of prolapsing, straining and trying to expel the egg. Right this minute, giving a calcium tablet would be a wise step. It will strengthen her contractions. The others have pecked her vent and she's now suffering from wounds that need treatment, too. Smooth on some antibiotic ointment without pain killer.
Since she has such a messy rear, a warm soak in a little Epsom salt and soapy water would be a good start. It will further cleanse the wound and relax her.
Warm some big towels in the dryer and place them in a crate with her enthroned on them. The continued warmth will help her and the warm towels will supply the moist heat she requires as her wet butt feathers dry.