I can personally attest to fact that texas ratsnakes willingly eat golf balls and porcelain eggs. I deal wirh them every year. And you are right; once they discover delicious eggs that dont run away or bite, they mostly leave the  rodents alone. And you are also correct thst snakes have a very strong sense of smell.  To ensure the fake "eggs" smell just like the real thing, before you place a fake egg in nestbox, first roll it around in a bit of chicken manure,& also in pineshavings, hay, or whatever bedding you use in coop & nest boxes. After a time, the fake egg will take on the chicken smells naturally, but if u are in a hurry to catch a snake, the above actions speed up the process.  Re broody hens & texas rat snakes, ive only had a snake steal eggs from under a hen once. (After that one instance i always put the broodys in seperate hardware-wrapped snake-proof cages.)  In that one instance, i didnt see the snake eat 4 out of 10 eggs that day. But when i  went to check on hen the next day, the 4 eggs were gone! And while broody hen was taking her quick daily break, and i was trying to figure out what happened to the missing eggs, i heard a rustle in corner of the barn. Hen got very worried look on her face, & immediately stopped eating & hurried back to her remaining eggs. It was the snake she heard, coming back for a second meal. She knew exactly what it was, even tho i had no clue until the snake appeared. That rat snake was nearly 6 feet long, & was trying to intimidate ME to leave, by posturing and rattling its tail. The instincts of a broody hen are very strong to stay with their eggs, even tho the hen is defenseless to stop the snake from eating her brood. In fact there are reports on this forum about large snakes strangling a broody hen and THEN eating her eggs. In those cases, suspicions are that the broody attempted to defend her eggs by pecking at the snake to drive snake away, & the snake then strangled her. So even tho she is as defenseless against a large snake as chickens are defenseless against predators in the dark, a broody will often continue to set on her eggs as the snake eats them from underneath her. She knows whats happening, but maternal instincts often prevent her from fleeing. After seeing how my broody hen reacted when she heard the snake coming back for its next meal,  I dont think your broody hen felt "ok" with the snake in the nest box with her, she was simply following her instincts to try and keep her remaining eggs warm & alive. And was wise not to otherwise try to defend against the snake.