We had a hen just recently also who had a prolapsed vent. She may be egg bound...the bath was good...but you need to check her vent to see if an egg is stuck. I vaselined mine up really good and her egg came out unfortunately with a large part of her inside vent. Keep the area as clean as you can...it will get infected quickly. If it appears to start weeping, red swollen...she is definitely infected. You must clean it and push it back inside the vent.
Preparation H will help to shrink the vent...but with my hen it did nothing because the prolapse was too great.
Good luck to you...