Your "jail" won't work ... WIRE CAGE will work but needs be be elevated at least a foot off the ground so air can circulate under her. Put her food & water in the cage, keep the cage in the coop. The longer she's broody, the harder/longer it will take to break her, I know went through this with 3 Blue Wynadottes last year. When they went back to their owner they went broody, she let them hatch which still didn't break them. She tried breaking them but it got too much work so she rehomed them.
You're in Australia so while our/USA weather is cool, you're in the Summer so it's warm & that's when they go broody, the warmth. I've heard of some putting ice under her, I've read about the cool baths but I know the WIRE CAGE elevated works, if necessary put a fan to cool her underside off.
IF you must rehome her, there are those looking/wanting broodies to hatch their eggs. Good luck.