Hi Terri, Welcome to BPO. My name is Heather and I have a St. Bernard named zoey.
As far as your fearful pup, the only thing you can really do is socialize. Since she has bitten, I would do it in baby steps. Start just by taking her on walks; if somone can pass by without her getting upset, give her a treat. The treat will re-inforce the positive experience, and more positive experiences she has had, the less fearful she will be. Also, don't let strangers pet her, at least not at first. When you feel that she is ready, you can help ease her into being pet by different people, but also make sure that she approaches them. If someone asks to pet her, tell them to wait and see if she is willing to go up to them; if she won't go up to them, she is not ready for them to pet her, and that will only add to her fear.