I'm so sorry that you are going through this. More sorry for Deja.

It's awful to be in a state of anxiety all the time. As your trainer said, it could be a number of reasons why she is in the state she's in. But it also sounds like there is a lot of hope. And a lot of work ahead. If the breeder is not taking her back, are you keeping her?
I got Buddy from a well respected breeder at 7 months old. He was a happy go lucky dog at her place. A dog cowering in the corner when we brought him home. Even in the car I could tell he was not at all comfortable. My husband had to carry him out of the car into the house! He wouldn't budge!
The good thing for both of us is neither seem to be a fear biter. I know Buddy was not. Not at all. That did worry me. Right from the very beginning with hubby having to practically drag him from the car. I was really worried Buddy would bite in fear. But he has ALWAYS been a sweetheart! But, like you, we had our work cut out for us. Well, it mostly fell on me, of course, because I was home with him the most.
It was months of work. Exposing him to a lot of things....NOT babying him........acting natural.....not coddling....giving treats at the right moments....giving treats to friends for him when they met him....teaching my husband how to pet under the chin instead of over his head, which made him cower (training hubby was the hardest part.

)
I did a LOT of ignoring, while keeping a watch on him out of the corner of my eye! He started out being quite fearful of my husband and I thought perhaps he had little contact with men. (I believe the breeder was divorced) It was frustrating as hell trying to teach my husband and Buddy at the same time. I'll never forget my brain storm in doing what I did when my children were little............When he came home from work, I would run to the door all excited and say, "Daddy's home! Daddy's home!!!"



And then have hubby BEND DOWN to his level and scratch him UNDER the chin.

THAT
worked! My excitement feed into Buddy and he soon was running to the door himself!
If I was working in the kitchen and banged pots and pans, Buddy would leave the room. I finally tethered him to me to keep him in the room and as gently as I could, went about my business as if I didn't have a wide eyed dog on the end of a leash.

Ignoring is the key. If you are constantly saying, "Its ok, boy/girl" they perceive it as 'being afraid/cowering'' is the correct thing to be doing.
He also would not walk through our barns. SO much scary stuff in there

and noisy too. I did the same tactic there. Walked on a leash and ignored. I made him face his fears but not in a forceful way. Just nonchalantly walked him through.
I could go on

but I don't know if you are keeping her or not. I just wanted to say, "I've been there." Maybe not as extreme, but I still get it. It's a difficult situation, to be sure. And if I'm not mistaken you also have small children? Your time may be limited in terms of working with this pup. It can be done, but I realize the road ahead is going to take a lot of patience and dedication. I wish you the best!