Hatchery BR, virtually zero. I have a 7 year old hatchery BR that has never been broody.
Now if you got a exhibition quality BR, they are broody as heck. And great mothers too. Mine went broody twice in one year.
Sounds like she may be thinking about it.
I've had hens that would screech or peck at me that never went broody - they just didn't like being disturbed on the nest. BUT the fact that your pullet is not laying, but has been on the eggs, plus the belly plucking - is an indicator that she is...