Slowly take her out, and socialize her more and more, just time will help this. She may never be outgoing, but you can help her feel more comfortable with others just with practice and practice. I would sign her yup for an obedience class, that will help build her confidence, and her trust in you. Even if she already knows some commands, the point with her is more experience with the world!

Don;t over react or scold her, or coddle her when she is acting fearful, ignore her and encourage visitors to ignore her at first, and let her make acquaintance at her own speed for now. And I'd be very careful if small children are visiting, and explain to them that she is a scaredy dog, so they should pretend she's not there. I have a scar on my lip from an incident when I was little, and a neighbor dog, Reggie, came to visit who was usually not allowed out of his yard - for a reason. I hugged him, and he bit me, right on the lip, and I was stunned! I remember my mother explaining "Not every dog is a hugging dog," and cleaning me up. In retrospect, I am sure Reggie was terrified!