Adoption day can be stressful for some rescue dogs. Homeless dogs come from various situations and abused, hoarded, or puppy mill dogs usually aren't well socialized. So when you put them in a crowd they don't handle it well. The shaking, hiding and nippiness you see at adoption day might not be a true example of their personality.
There are two ways to handle this situation. Stay and hope she eventually relaxes, gets used to the crowd? Or take her home and let her hide in her bed for the rest of her life? We compromised. I kept Corona in my arms, stood in the back behind the table and away from the crowd.