You need to stop the hen laying if its in with a chance of getting better, and I do know its possible. The best way to do this is to put it in a dark place, and just bring it out for feed and water. Hopefully it will stop laying. If it keeps laying, it will all pop back out again. Stopping infection is hard too. Sugar on your finger, gently push it back in, and hopefully the sugar will stop it coming out again. You need to keep it clean, thats important.
I have been lucky and not had many prolapses, no, not me, I mean my hens..... in fact cannot remember the last one, until last week, and that died. But it was a bad one!!