Bad broodies but great mamas
My polish was broody once for all of 15 minutes...
It was a normal day and my polish decided to be broody. I noticed this when she was rolling the other polish's egg under her like a broody. I rushed into my other coop and grabbed some fertilized eggs and brought them to my polish broody. She rolled each egg under her. I decided to leave her alone. I checked on her 10 minutes later and she was walking around normally.
So forgetful

...
I recommend you wait a week or two then buy some day old chicks and give those to her. It would be cool to see if she lasts the full 21 days, though.