Wonders if she's ready to lay and not quite ready yet.
https://www.backyardchickens.com/articles/who-is-laying-and-who-is-not-butt-check.73309/
Is she in the nest all night too?
Is she being bullied at all by older birds in the flock, and maybe 'hiding' in the nest?
Is she getting up to eat, drink, and poop?
Not likely that a bird who hasn't laid yet would go broody.
These are my go-to signs of a broody.
Is she on nest most the day and all night?
When you pull her out of nest and put her on the ground, does she flatten right back out into a fluffy screeching pancake?o
Does she walk around making a low cluckcluckcluckcluckcluck(ticking bomb) sound on her way back to the nest?
If so, then she is probably broody and you'll have to decide how to manage it.