I had one who would NOT break - we're talking WEEKS in broody jail, ice, fans, etc. I even tried giving her chicks. Nope. She rejected them and went right on brooding. What finally worked was setting up broody jail in my bathroom. I think being completely out of the coop worked.
Might have been cooler there too?
I had a serial broody one summer, had to move the breaker crate several times a day to keep it in the shade during a heat wave, I think the change of scenery helped break her....
...tho not for long. After breaking her 7 times, after her hatching in March, I finally gave her away, she never went broody again. SMH.
It can take tenacity and creativity to manage a breaker crate.
I finally got the 'perfect' set up with a feeder that lasts and won't spill.
Using horizontal nipples made watering easy.
The cup, with hanger wires bent so they won't knock it down, is for a handful of scratch every morning(just like the rest of the flock gets).
My experience goes about like this: After her setting for 3 days and nights in the nest (or as soon as I know they are broody), I put her in a wire dog crate (24"L x 18"W x 21"H) with smaller wire(1x2) on the bottom but no bedding, set up on a couple of 4x4's right in the coop or run with feed and water.
After 48 hours I let her out of crate very near roosting time(30-60 mins) if she goes to roost great, if she goes to nest put her back in crate for another 48 hours.
Tho not necessary a chunk of 2x4 for a 'roost' was added to crate floor, gives the feet a break from the wire floor and encourages roosting.