I loved watching your video - it was really well done. I laughed to myself, thinking it'll be months and months before any of my girls would go broody.
Hah! One of my girls was channeling your bantam Sophie this morning! I couldn't believe it. I had never seen a broody hen before watching your video, and here was my girl, doing the exact same thing. Too funny.
I stole her egg and put an ice pack under her. I checked on her 20 minutes later and darned if she wasn't trying her shivery best to hatch out the icepack. (I took the ice pack away since it was 20 degrees this morning.)
Basically they suggest simply forcibly removing her from the box and then blocking it off so she can't get back in. You might want to try taking out the golf ball for a few days too...