NEVER give treats or praise when she acting fearful. Personally, I would have her sit - this gives her something to do, whereas the word "calm" does not give her a clear picture of what you want. You might have her "sit" first, and then "calm". At first, give her the treat after she is calm for about 3 seconds. As time goes on, she has to sit and be calm for 10 seconds to get the treat, and so on....until you no longer need treats. Just take one baby step at a time.
I am horrified at this "trainer's" suggestion of correcting her for being fearful. This is the worst thing you could do. Your dog is not being "bad". She is traumatized, stressed and afraid. The analogy Carina made about being punished for fear is right on the money!
Your dog may never be the bravest dog in the world, but with patience and consistancy, she should vastly improve. She is only a puppy and CAN learn that she has nothing to fear.
Nothing can be accomplished until she learns to trust you and to know that you will not put her in any danger!
OH, and thanks for saving this girl!