One of my dogs is a very alert guardian and will run barking ferociously at people walking by our home (if my other dog is present) but will not get within 10 feet of them. But she is also very timid until she warms up to someone. She also will wedge herself behind or under furniture at times or stand under my legs if I'm talking to someone she isn't familiar with.
We got her at 9 weeks at the pound and I don't think she was abused. Maybe this is just your dog's personality? Maybe socialize your dog often, if possible. Take her into the pet store, to visit people, etc. Princess L, knny and others may have more knowledge to comment on this.