I went to see Sophie the next day. She was sleek and glossy... and cuddly. That timid cat who was frightened of everyone but me had been replaced by a cat who demanded affection from every primate within reach. Apparently what her little fluffy brain needed was, um, more trauma.
Other cats I've fostered have been similar. At each move--shelter to foster home, foster home to forever home--they've become more open and loving. It's like they needed exposure to change to learn that change isn't bad, or to encourage them to depend on humans more. Cats are indeed attached to familiar locations, but maybe we shouldn't be quite so worried about moving them to new homes.
(Mind you, spending several weeks on the streets in a coyote-infested neighborhood in cold weather is extreme. Not Recommended.)
Miss Sophie beat the odds. Bless the woman who kept her fed and returned her to us. I hope Sophie's new owners appreciate what a wonder she is.