Sorry, It has never occurred to me to WANT a sitting hen.
I have about 25 Silkie hens and I have one or five sitting at all times.
Phoenix and Sumatras go broody when they are 3 years old and stay that way winter, spring summer, fall.
Wheaten Ameraucana hens are the same color as new shavings. I did not even see that hen tucked into a corner until she had 8 little fluffs following her around. I hate little ones outside in the middle of winter.
Yesterday, I pulled a coil of extension cord off the top shelf in the barn and got a face full of eggs and a mad Sumatra caught in my hair, I have scratches all over my face and neck. My husband looked at me, shook his head and said "I don't want to know"
Last summer, I was walking through the barn and a baby chick popped in front of me. OK that's odd. I stopped and contemplated for a moment. Another landed in front of me. My brain clicked. They were falling out of the rafters. I raced up the steps and tried to find the nest.
By the time I found it, 12 chicks had landed on the floor, but Mamma was too big to get through the hole they fell through. I had to herd her to the steps. She got down and attacked the great Pyrenees that thought chicks just appearing from nowhere was interesting also.
I have no Idea what makes a hen sit
Put her in a cage with a nice cozy nest all closed in and dark inside and put the eggs in the nest and see if she takes the bait.
Sometimes they will cluck for a week before actually sitting.