Perfect. I think it is the combination of hormones that say "MUST HATCH SOMETHING" and the ability to stay hot underneath that keeps them broody. I don't know how to get rid of the hormones directly so removing the ability to stay hot seems to be the path.
Your mentioning her "poofing" matches what I see in some of my hens. Almost like a "tick" as Dr. Jekyll turns into Mrs Hyde.
Well it seems to have worked. 2 full days in the hanging jail cell and she seems to be back to normal.
We let her out last evening, but put her out in the yard with the other hens. I locked the coup door so she couldn't get in. She was doing typical hen things w her flock for about 2 hours. I put them all back in the barn and she didn't even try to go to the nest box. I checked on her after dark and she was roosting w the rest.
This morning she was doing normal hen things, so I think we are ok (for now!)