Buff Orps are famous for being broody. They make great sitters. She is probably entering a broody cycle. I had a buff as a poop spreader, she was old and I took her out of the laying coop and put her in the horse pasture with the other culls. She went missing for more then a month, then I found her one day under a tree, half dead sitting on a nest that all of the spreading hens, must have been laying in. There had to be 40 eggs in that nest and from the smell they were all rotten, but she wouldn't leave that nest. Had I not found her she would have sat there and died before leaving that nest without a hatch. I managed to get her off of it and gave her to a neighbor to sit his eggs.