Could Nelly be broody?

Nelly, my ex batt, has been behaving quite strange last night and today. She's not been hanging round much with the other 2, I found her once in a nest of leaves in the play house, turfed her out and she went and sat in the nest box, hunkered down as if laying and not wanting a bar of anyone or anything. She's had a full crop at bedtime, so she's been eating, but she was still in the nest. She doesnt seem ill, still bright and alert, just...erm...not Nelly??? She did have yolk on her foot and there was some on the coop floor as if an egg had been layed while roosting, checked inside Nelly and there's no sign of a broken egg...no egg at all actually. Could she be having a weird broody attack..she was crowing like a cockerel a few weeks ago, could it be a hormone thing due to getting on a bit, or is it more likely she's getting ill. I'll start worming tomorrow again, there's no mites or lice. Puzzled??