I've only ever had one that was that persistently broody. One hen doesn't bother me and she
could come in handy when I want to hatch some more chicks~IF she is a good mother and can complete a hatch well. Mine didn't. She died.
If just tossing her off the nest every time you see her doesn't do it~ just your average broody I've broken with a dunk or two in a water bucket~"OOOOhhhhh! How cruellllllll!!" I know, I've heard it all.
I just pick her off the nest, carry her to the water bucket by her feet, dunk her a couple of times and toss her out the coop.
No, the water isn't cold enough to change her hormonal drive or the temp of her body, she isn't in the water long enough to make any temp difference...it just makes her agitated and changes her mind about being in the coop right then. Her thoughts probably? "The big person could possibly surprise me and dunk me again...think I'll stay outside a while."
I'm not convinced that isolating them in a cage without nesting materials or putting them in time out has anything to do with cooling their body temps and consequently changing their hormonal urges...I think it has mostly to do with the anxiety or agitation of being separated from the flock. I believe this agitation has a way of switching the bird into survival mode instead of Mommy mode.
Being lifted from a comfy nest, hung upside down and dunked in water is just shocking enough to make a hen mad...you know, madder than a wet hen? Probably where the expression comes from....I've never seen angry hens standing out in the rain getting even more angry~so simply being wet isn't the source, I imagine.
This is, IME, by far the quickest and most effective way to break a casual broody. A career broody is another kettle of fish and this method just won't work on her~neither will isolation from the flock, isolation in a wire bottomed pen, etc. Then you have to decide if she is worth her weight in feed to be a mother for future birds. If she is not an exceptional mother, my advice is to cull.
