Sorry, I have no expert advice to give, but I'm having a similar problem. Here's my routine, everyday, sometimes a couple times a day, I go out and take her out of the box and put her in the run. I have a llttle wading pool of water and I'll stand her in that and sprinkle a little water on her. Then, I throw out some scratch. She will usually jump out of the pool and start scratching around with everyone else. I also let them free range, so sometimes I take her all the way out of the run and set her out away from it. Some days are better than others, and she only has to be taken out once, other days, it's an on going thing, and she's getting pulled out of their a half dozen times or more.
I have even had to take her out of the nest box and put her on the roost with everyone else for the night.
I'm sure if I didn't she would spend the night in there.
I'm hoping that one of these days, I'll go out to collect the eggs and she won't be on the nest anymore. Then I'll consider her cured of her broodiness!
I haven't gone as far as to make the wire bottom cage and isolate her yet...I haven't gotten sick of my routine quite enough to build the cage for broody busting.
Buy that is the method most have said will work, a wire bottom cage and her put in it for a few days.
Good luck!