Hello there and welcome to BYC!
I am so sorry about your hen!
You will need to soak her bottom good and get all the crud off of her. Use a mild detergent like Dawn or something in warm water. Usually if you put them in warm water they do relax a bit. She may not like it, but she needs to be clean.
And it all needs to go back inside her before it becomes too swollen to get back in. Use Prep H on the entire thing and push it back inside, directly straight back. Put more H all around her vent area. If you need to trim back feathers, do so. And keep checking and pushing it back in each time it comes out.
Then keep her separated and inside the house or in the barn away from the others in a very clean dry place. Make sure her bedding stays very clean or even use towels as you don't want crud going back inside with her. Keep her in low light, just enough to see and eat. And only low light for about 8 hours a day. What this is going to do is either send her into a molt and make her stop laying and or shut her laying machine off. You can't let her lay until this heals or it can kill her. So low light for about 8 hours a day, the rest of them complete darkness.
And no other birds with her as they can peck and kill her with her insides hanging out. This can take several days to a week for the swelling to go down and for it all to stay inside of her. I would feed her every easy to digest foods and offer up vitamins as well. Calcium too. The vitamins will help her keep it inside too.
Good luck and I hope you can get this sorted out soon!