I am not in the home to see the dog's behaviors, so take what I say for what it is - complete spitballing...

I had a rescue that I named Shyner. She was afraid of everything. She was found running loose out in the country, and after a month with no claims on her, she was officially "ours". She was about a year old, at the time...

Shyner would shut down when there were loud noises, if she had to get into the car, if someone walked directly towards her, etc. She had little food drive to start, and never did play with a toy in the 12 years that we had her. Training her was difficult to say the least...

"In the beginning, her training reward was to stop training. The one thing she wanted was to be done with training so when she did something right, that's what she got. Needless to say, training was slow, but this way, she knew that the way to stop me from doing what I was doing - to get the pressure off, was to do what I asked. She also learned that working with me wasn't the end of the world These sessions were extremely short - simple things like sit, or down, look at me when I say your name were taught - nothing complicated. Once she began to offer behaviors, I was able to incorporate praise as her reward. She never did work for food or toy rewards - didn't care for them."

That is exactly what we do here, we only ask him to sit at doors, and before being let out of the pen. At meals I just stand there until he sits, because if he is laying down or if you speak, he will not get up to eat, making him sit always ends in him eating all or more than half his food. We did cut off any other training, and prob will not bother with anything more than basics in the coming years.
"She also learned how to be a dog by observing and interacting with my other dogs. They modeled the proper behaviors to her, and slowly she began to take her place in the pack. I have to give credit where credit is due, as my dogs have always been very accepting of other dogs and are great behavior models."

I have been very tempted to get a second adult, even just for my own sanity...I got a dog for the company while I stack and split wood, walk, shovel, fish, etc.

"Shyner was never once corrected with anything harsher than a "nope" in a lower than normal voice. It took me over a year to crate train her. Every step Shyner took required time, patience, and consistency. Lots of time was spent just developing the bond - sitting with her talking softly, giving belly rubs, ear scratches, etc. She used to hide behind the bed - between the bed and the wall - when she was scared. It was her place, and I never took it away from her - even when she started going to the crate, once in a while, she would go back the the bed."

I have always left his crate wide open. He hasn't quite found a place in the house, besides scraping paint off my walls. He refuses to walk anywhere in the house, and ends up laying in the room closest to the porch. He has never tried to explore the house, and even tho I am going from room to room daily, he never follows.

Watching her slowly open up and be a dog was worth every single painstaking step, though.

I think for dogs like Shyner, something like Rescue Remedy may have been helpful - just to take the edge off the stress and get her into a learning state of mind.

Just my experience...