I would start smaller than a dozen, but it’s up to you. And join the September Hatch-a-Long
Here’s the link:
https://www.backyardchickens.com/threads/🍁-september-hatch-a-long-🍁.1406610/
Your standard chicken?
Yes, she could hatch chicken eggs. Probably 10-12. If she’s a new broody and never had chicks before I’d recommend doing no more than 5-7 eggs because it can overwhelm them having too many their first time.
I would not do it with a standard chicken, they are way too big and will crush the eggs. You need a bantam to sit on them.
Here is my bantam. She is very small and had 10 eggs (2 chicken and 8 quail). All of them hatched!