Spangled -- I had a broody once that I had tried to break up for months. Finally, I bought some day old chicks to put under her. I put them under her after dark and intended to leave them there. The way she growled, nay, screamed at them when I put them there made me nervous, so I went out to check on them just before daylight the next morning. She had pecked a gash on one's head and left them in the nest. She was sitting in another nest box when I got there. I fired up the brooder and put the chicks in to warm up. I tried once more but it was no use. She wanted nothing to do with the chicks, she just wanted to sit.
My nest boxes are inside the feed area of my coop and have entry doors to the coop, and collection doors to the feed area. The top of the boxes make a handy shelf that I use for my stage one brooder area. I put the chicks there and brooded them as usual. The chicks were growing well and the hen was still happily sitting on some golfballs in her original nest just under the chicks.
Two weeks later, I went into the coop and looked into the nest she was in. She casually walked out of the nest, out of the coop door, around to the people door (into the feed room) and inside to the brooder. I followed to see what she was up to. She flew up to the top of the brooder and jumped down inside with the chicks. Scared those (now big) chicks silly! I thought she was going to peck them but instead, she started squatting, and clucking and trying her best to get them underneath her! LOL! The chicks wanted nothing to do with her, so I removed the lamp (it was cold out) and soon they went underneath her to keep warm.
She fretted and tried to mother them but they never minded her too well. She followed them, not vice versa. When they got separated, it was she that panicked, not them. They finally learned to come to her when she called them to a treat, but not too fast and not all of them at once. She got tired of chasing them and trying to protect them in about three more weeks, but by that time, they were fully feathered and barely fit under her anyway. I felt sorry for her, but it was interesting to watch!