Do you have a rooster so she could be sitting on fertile eggs in the bushes somewhere? The one time I had a broody outside the barn and fenced area (I was letting them out during the day) I figured she was gone but saw her a couple of days later dustbathing. BUT she didn't come to the barn that evening. We "found" her at 3 AM when she was screaming. A coon had found her and ran up the nearby tree when we ran out. Her nest was in the bushes right near the little barn which is maybe 20' behind the house and the nest not more than 40' yet we had no idea it was there.
I don't know how far your birds go from buildings, I've never seen mine more than 100' from one. Might be worth a thorough look through all the bushes and other potential spots.