That's a two part question really. Depends upon if the egg is still inside when she's prolapsed. If so, you'd treat it like an egg binding, which would suggest a warm bath to 'relax' the muscles and a calcium supplement to strengthen her contractions. If she's passed the egg, but her vent is still outside instead of inside, give her a warm bath to ensure that the vent is clean without rubbing or otherwise abrading the tissue more than the egg already has, then gently tucking the vent back into her. Remove from her bath, and blot her dry with a terry towel, then apply honey or triple antibiotic without pain relief onto the vent to keep it moist. Moist vent tissue can heal, dry vent tissue will die. Dead vent tissue is disastrous. Keep an eye on her. She's a young, recently started laying hen who is still getting all her girly-bits to play nicely with each other. It sounds as if she's laying larger eggs than her body is prepared to easily accommodate. It's very likely that she'll outgrow this problem, given her age.
