Poor dear!
I agree, it does sound like she's struggling to expel an egg.
She may have some pressure on the nerves in her legs which could cause her to have difficulty walking.
I would get the Calcium into her. If she's not lethargic, you can try a soak in a warm epsom salts bath or place her on a heating pad, just monitor her that she doesn't get too hot on the pad.
Keeping her hydrated is important too, so if she's drinking, that's good.
What do you feed including treats?
https://www.backyardchickens.com/ar...ng-from-vent-prolapse-oh-my-what-to-do.76124/