What was her history? Is she a rescue?
If not, what's the breeder say and how are the littermates? The reason we take the months to research and get a 'responsible' breeder is to have the lifetime help with situations like this.
If you rescued her and don't know history or have breeder help, have you seen these sites?
Helping The Shy or Fearful Dog « Homeward Trails Animal Rescue | Pet Adoption in VA, DC, MD
How to Fix a Timid, Shy & Scared Dog | Dog Care - The Daily Puppy
Shy dogs/fearful dogs links and resources
I've heard that this helps WITH training/management/PRO-active work ---> Thundershirt | The Best Dog Anxiety Treatment