If it were me I'd give the dog more time to settle in, learn what it's like to be in a home and have owners, and some training before I threw in the towel. No one knows this dog's background. She could have been abused by a man for all anyone knows, and that's why she acted so fearful of your SO and the male vet tech. It could be as simple as all the change is overwhelming her. It seems like she's getting better from what you've observed, laying at the top of the steps and waiting now. Another couple of weeks, who knows?
OP, FWIW my cat hid in the bathroom for the first two weeks I owned him and hissed and cowered when I'd come in. I thought he was going to be a scat cat that would only come out to feed and go to the bathroom and watch me and my other cat from a distance.
HAHA. Fast forward four years and he's super charming, gets into everything, meows at me like he's chatting with me, sleeps on my bed at night, and plays hard with my other cat. Mr. Frightened turned into Mr. Personality Plus, and I absolutely adore him. If I'd have given up cause I wanted a snuggle bug right away and didn't give him time, I wouldn't have this wonderful animal.