I wouldn't recommend doing anything to block the vent. She needs to poop and if there is still material blocking the oviduct, it needs to be able to come out.
Continue the calcium for now. I've had lots of experience with prolapse. The longest it took for the prolapse to resolve and finally go...
Encourage her to drink. Dipping her beak once in the water will remind her she's thirsty. In her exhaustion, it's typical she will space out and forget to drink. Soon, without drinking, she will become too weak to drink and too weak to push out the obstruction.
When your hen strains it means there is an obstruction, which can be an egg with a hard shell, an egg with no shell, a collapsed egg. It can mean there's tissue that sloughed off the oviduct wall, or it can mean tumors which can't be expelled. If the obstruction is tumors, these are your hen's...
It helps to warm up towels in the dryer and put her into a crate on the warm towels. The warmth will relax her so her pelvic muscles aren't fighting against her contractions, but working with the contractions.
The blockage affects how her fluids are dispersed into her body, so this ordeal can...
She needs to have the whole Tums. Putting in water dilutes it too much for it to do any good. Get another Tums and break it in half, Pry open her beak and stick one half in, let her swallow, then stick the other half in. It takes a minimum of 500-600mg calcium to trigger adequate contractions...
Read this and you'll get a better idea of what's happening to your hen. https://www.backyardchickens.com/articles/stuck-egg-collapsed-egg-hanging-from-vent-prolapse-oh-my-what-to-do.76124/
Prolapse is about as serious as it gets. Your hen likely had others peck at her prolapse and that's why...