Maybe take her to a puppy park, or somewhere that she can get socialization with other dogs and people. Should be a big help. Good luck, and start with baby steps. Don't get her overwhelmed.
It's my opinion she has naturally fallen into the "Omega dog" role. (In a wild pack, the Omega is the lowest-of-the-low, subservient to all the others, and often the one who is a scapegoat for the rest of the pack.) It's strange - I was reading something about this in a wolf pack only a couple of days ago....
In the case of the Omega Wolf in the book I was reading about wolf behavior, she had a hard time of it for ages and ages, then suddenly came into season and was chosen by the pack leader to be his mate! That elevated her status -literally overnight- to Alpha female! And she fell into that new role quite happily, seeming to forget her earlier "untouchable" status!
Like a fairytale ending (servant marries a Prince and becomes a Princess!)
Now I wonder if there might be some way of adapting that (true) Wolf story to your little one?
I wonder if allowing her a certain privilege (such as being allowed to sit next to the "Pack Leader" (either you or your husband, whoever you feel may fit that role in her eyes)....on the sofa? Or being allowed on the bed...or eating at the same time as you, in the same room....or something similar might "up" her status?
You are going to have to be quite careful you do not reward her in any way by showing favours or giving her treats at those very moments she is behaving subserviently or cowering. As far as a dog is concerned, you would be giving approval for that behaviour if you were to do that. It might be best not to give her affection at those times either, for that means the same to them. But to gently ignore her.
If you catch her in a moment when she's "coming out of her shell", just gently stroke her, or say "good girl" in a gentle encouraging way. And if you do decide to do anything to lift her status, choose a moment to do it when she seems relaxed and a lttle more outward towards you.
From then on, it's a question of balance. You don't want her completely switching either, and making a takeover bid, as dogs can do in a "pack". That can result in nervous unstable behaviour, or lives made a misery by the dog! But I guess you and she will find a middle way.