Letting them "wait it out" is animal cruelty in MY opinion. They have hormones that are telling them to hatch eggs. They have nothing to hatch. Those hormones don't just run 21 days (normal incubation period) then dissipate. The "I'm incubating" hormones change to "I'm raising babies" as soon as the chicks start to hatch or they wake up in the morning after you shove some day old (or a bit older) chicks under them when the hen is ASLEEP AT Zero dark thirty. Pitch black, not a bit after twilight. Don't try this mid day and use the dimmest flashlight you have with just enough light near the hen to tell front from back, slip the chicks in one at a time FROM THE REAR under the hen's wings. When I did that 2 years ago my broody hen "hatched" 7 chicks overnight from 3 plastic eggs. No longer had any interest in the nest box and raised them for 8 weeks. They do not think about this stuff real hard
A hen incubating eggs WILL get off the nest to eat and drink. I have never observed a broody sitting on plastic eggs or only shavings get off the nest. The first thing mine do when I put them in the broody buster (elevated with 1/2" hardware cloth bottom) with food and water is go straight to eating and drinking. If I just take them off the nest they run right back, if excluded from the nesting boxes, they go nuts trying to get back in.
With regard to the cold water bath, I say Bah! I had a broody hen thaw not one but two refreezable ice packs in succession. She was still a furnace underneath. They just put out more heat to keep their breast area warm enough to incubate. As long as they can trap that heat against something (the nesting material) they will not cool down. So where is this heat coming from? All that food they are
not eating. So where is it really coming from? Their body stores which they are NOT replenishing.
As such, letting them stay broody with no fertile eggs to hatch does them not good, only harm, as they don't eat and drink properly. They might be fussy in the buster but they eat, drink and not being able to stay hot underneath causes the hormones to subside. In warmer weather this can take many days, in cooler weather I've had them break in a couple of days especially if I caught them early in their broodiness - meaning the first day.
The longer they have been broody on the nest the longer it takes to break them. Start now, leave her buster box with the other hens. I've not seen a change in "social status" when a broody hen is being broken or when she returns to the flock on her own 2 feet.
Guess I'll give them a couple eggs from another pen. 
