As of this point, I had read enough and learned enough about weather and chickens that I can let go and let Buffy sleep out overnight. She made it into our yard without knowledge or food or water. She survived long enough to find a little shelter, get along without specific food or water, though I don’t know how long she’d been chicken wandering. And now she has a coop, water, food, and we’re probably ready to pull her back in the house if it seems too cold.
And it was okay.
She quickly put herself away for the night and pretty much laid an egg a day for the next week or so.
The cats remained jealous that she got to be outside and she continued to want to come inside. But, as the chicken diapers hadn’t yet been delivered, I was comfortable letting her acclimate to the outdoors. 
Buffy exploring the un-refurbished tiki bar (between seasons).
Accidental Chicken 