You've got to clean it and get a good look at it (and then post pictures, please).
I would wrap her front half in a towel to calm her down and prevent her from flapping... plus, it makes it dark, so she should be relatively still. Grab some saline (table salt + warm water) or just clean water and wash her bottom! Use a paper towel and squeeze water over the wound. Once you can see your way clear, wipe anything away that you need to. Be gentle... if the skin is broken, we don't want to hurt her.
If washing reveals a prolapsed vent or a peck wound, treat it just like you would if you had a skin injury. Rinse it, dab some antibiotic ointment on it, and keep her comfortable and isolated from the rest of the flock until she heals. If you discover a prolapsed vent, follow the same treatment, but add a little Preparation H to her vent and gently nudge it back in to place. Within a few days or so, you should see improvement in the area. Keep her inside until she is FULLY healed. If there is any redness or inflammation, the other chickens WILL peck her and make it worse........ as you can potentially see here. :/
Has she started laying yet? If so, have you felt her abdomen for evidence of an egg (especially a crushed one)?
I would go ahead and put her on some water-soluble oxytetracycline, too... With an open wound in that location, you are talking infection CITY, and *that* is what we need to avoid if possible. The antibiotic won't hurt her and you can put it in her water. I got mine at our local Livengood... I've not seen it at
Tractor Supply, but a feed store SHOULD have some type of water-soluble tetracycline. If you can't find that, you can give Tylan 50 (also good for respiratory infections and available pretty much every where) orally using a syringe dropper (dosage unknown)... but the water-soluble powder wins. It may be in the goat/cattle section. I believe it's 1T for a gallon and 1/4T for a liter. The bird will dose itself as long as it is eating and drinking properly.
If she looks like she's chilly, put a heat lamp by her... Also, for tissue wounds, it can't hurt to offer her high-protein foods like boiled eggs and meal worms.
Keep us updated!!
MrsB