Poor thing. I wonder what her past was like. Did they have kids in the house...if they did maybe they were too rough with her. That seriously makes me sad
But I did have one like this..when she first came. She was so shy and nervous but I worked with her and she outgrew her shyness...she even became feisty! lol You just have to work at it, it will take time. Maybe a long time..up to a year for her to trust you and not be so afraid. You have to be gentle and tell everyone else in the home to be gentle...don't yell ever, be very quiet around her..don't pick her up, let her come to you. There's lots of things that can help, and also take her to doggy playdates with other nice dogs.