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?
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.
BUT....how old is she?
Can you post a pic of her?
I doubt she's broody, but she may be getting close to onset of lay so spending time in the nest.
There's always this......
https://www.backyardchickens.com/articles/who-is-laying-and-who-is-not-butt-check.73309/