Are you sure she's not broody? Australorps are known to do so. She sounds like she might be to me. I've had all four of my silkies hens and both bantam cochins go broody on me at least once. They pluck their feathers out of their breasts so that their skin will be in contact with the eggs. They will stubbornly sit on their chosen nesting place, even if they're brooding nothing. The way they sit is not the usual way you see a chicken sitting down. They'll be flat, kind of like they deflated a bit. If you bother them, they may growl, peck, or lower their heads and spread their wings a bit to try to scare you off. Some of mine come down with a case of "jelly legs" when they're broody. My blue silkie hen will just sink back down into a broody hen sitting position if I take her off her nest. Even if I throw her out in the yard she'll just sit there until one of the other chickens starts to bother her. Broodies also spend most of the day on nests, so they're not out eating and drinking like normal. They will lose a bit of weight because they'll get up only once a day to eat, drink and poop.. Best way to tell she's truly broody and not a sick, lethargic chicken? Keep her inside for a day or two. Watch for her to produce the biggest, nastiest, smelliest poop you will ever experience as a chicken owner. That's broody poop. You can't mistake what it is. I canguarantee that.
If she is broody, there are threads on here on how to break a hen of broodiness. I'm trying to break five broodies right now without the use of my broody breaking cage. I usually set that up in the garage, but my husband is refinishing all the woodwork in the house, so he's staining and varnishing all the doors and floorboards out there. Thus, I'm stuck evicting them all from their nests three times a day.
