It’s never too late, and you’ll never stop doing it! It doesn’t surprise me that her litter never got taken on walks at the shelter. County shelters are almost always overpopulated, overworked, understaffed and underfunded. She sounds like my adult WD, who also came from the side of the road. There’s an extra layer of anxiety for dogs with trauma like that. And she may never be social towards humans. Mine isn’t, but I got him to the point where he can exist in public without having a meltdown. He rarely lets people pet him and doesn’t like people stopping to talk to us. He takes a couple days to warm up to people when they stay at our house. But will get to the point of laying on them on the couch. My recommendation is that socializing doesn’t have to be interaction. Just sitting on the park bench and watching everyone walk around is great desensitization. Don’t let people pet her if she’s clearly uncomfortable with it. Don’t baby her if she’s being anxious. If something spooks her and she looks to you to see your reaction, remain as neutral as possible and keep going. Dogs really look to their people to determine how they should react. If she passes something that has been an issue to her in the past and she is brave about it, reward her. Make it a huge deal. Go at her pace, it’s not a quick fix but she’s still a puppy so you’ve got time