Everything I read said Sebrights rarely go broody. Guess my little Sebright, like yours, can't read.
Each day I would laugh as I removed a HUGE 2.8 - 3.0 oz egg out from under her. (I have mostly big birds & of course our roo can't possibly mate with tiny Trouble.) After a week of stealing her eggs & kicking her out of the nest, she began sitting on imaginary eggs. That's when I finally broke down & made her a broody apartment. I gave her 2 of the smallest eggs I could find & she's been happily sitting on them for a week now.
thats precious! Yes, mine were very broody too. I adored them, just not safe for them here.