She's back!!
I came downstairs to make breakfast, and get started on research again, and I found her, I mean, I found Willow. She found her way home to me. Miss Kitty Fantastico was crouched next to her, licking her, and I shooed Miss Kitty away as best I could, and helped Willow up, wrapped her in a blanket, and got her to bed.
She's been sleeping. However she came back must have drained her terribly. I've been standing watch, sort of. I can't even really bear to leave the bedroom right now.