Is she able to poop?
I'd make sure she's staying hydrated, offer her wet feed. Get a little coconut oil into her (about 1/4 tsp twice a day).
If it's not protruding more than that, I would be hesitant to push it back in. I'd try giving her a warm epsom salts soak to help reduce inflammation. Dry her very well so she doesn't chill. A hairdryer works well in drying the fluff. Once she's dry, put ointment, oil/vaseline on the vent and any exposed tissue to keep it moist. An anti-inflammatory cream would be good to use if you have it.
Since it is prolapsed slightly and of course red, I'd keep her separated from the other chicks so they don't pick at the tissue. This can cause damage.