timid american bulldog

Question
I purchased (rescued) a 6 month old female American bulldog from a pet shop.  She is great with other dogs at the doggie park and actually usually the center of attention while running around.  My problem is she is is terrified of people, except my girlfriend and her mother who actually picked her up from the pet shop as a christmas gift for me & myself, and will do everything she can to stay away from them.  While walking her she will pass people at a few feet distance, but as I approach someone she cowers away.  Is this a permanent thing or will she grow out of it in time.  Also do you have any suggestions.

Answer
OK, first thing is to get the dog into an obedience class right away. This isn't something that can't be turned around, yet.

When strangers approach, ask the dog to sit and let them pass. Don't give her the option of avoiding them.  First and foremost, she has to totally trust you in order to feel safe in this situation.  The more self-confidence you can instill in her, the better.  Obedience class will give her a structured environment where she can learn and feel safe as well.