Looking for some advice from anyone who's adopted a rescue animal. Our previous dog passed away last November (I had her for almost 18 years) and we think we're ready to adopt again.
Lucy is a 1-year-old terrier/poodle mix who was rescued from animal control in San Jose after being picked up as a stray. We met her at an adoption fair and are currently on a 7-day trial adoption run to see how she fits in with our lives.
But we've run into some issues. Lucy was fine around small dogs and strangers previously - at least at the adoption fair. When we brought her home and started walking her around our neighbourhood, she was skittish around big vehicles and big dogs and just wary of strangers (she would stop walking, watch them walk by, then continue walking). We introduced her to my mom and everything went fine.
But after a somewhat scary experience for her at our vet during a checkup yesterday (she's never been there before and she started trembling the moment she entered the clinic), she's now started growling at strangers during our walks. I tried to introduce her to some coworkers and she growled and snapped at them. She even growled at me this morning after I appeared from the bedroom (though when she realized it was me, she became happy/excited as usual).
Is it possible that her experience at the vet just brought back bad memories of being at animal control and she'll go back her old self after a day or two? Or is this a sign of something else? Where/who should we go to in order to help her with stranger/dog socialization if she doesn't improve with time? Is this something that we have to expect with adopting from a rescue?
At home, Lucy is a great dog... if somewhat possessive (still learning, I suppose) but cuddly and loves stealing socks. But given recent developments in her behaviour, I'm not sure if we should still forge ahead with her or return her to the woman who rescued her.

We feel totally horrid for even thinking about doing that but the thought of dealing with a scared, growling, barking, biting dog on each of our walks makes us hesitate.
Thanks.
Lucy, the sock stealer: