We had.. well still have to a degree the same problem with Lola. She trust noone. Heck when we first brought her home she avoided us all like the plague. She bonded with Bubba first. I wish it would have clicked then.. but I figured she was just shy.
As she matured we started seeing dog aggression (fear and dominance based) and growling and barking at strangers (fear based). We took her to a behaviourist. It definitely helped a great deal. I can now take her in public and to the vet without too much fuss. Regarding strangers she still will not allow just anyone to pet her. People can look at her.. talk to her but no touchy touchy. She starts off with low growls and quiet barks and now that I know her triggers I'm able to correct her and stop it before it even starts.
You definitely need to get her out and about. I used a gentle leader at first so I had head control with Lola, even though she never attempted to bite anyone I didn't want there to be a first time. Start off at a distance Kalli is comfortable with and gradually move out of her comfort zone. My trainer had me bombard her with treats if she was sitting quietly and watching people without reacting since Lola won't take treats from strangers. Plus noone was willing to try and give her any. It helped her associate strangers with treats to the point where she would see a stranger or another dog and then look to me for treats.
At our last vet visit a young Boxer pup decided to 'box' Lola on the head as we walked by. Her hair stood up, but no barking or growling she just kept walking.
That's a huge improvement of what would have happened in the past.
We've had a couple set backs.. dogs off leash charging up to her.. people not listening to me when I say she's fearful of strangers to give her space. I've heard 'All dogs love me' more times that I can count.
Just keep at it.. she will get better. It's a slow ongoing process. Lola still doesn't love strange dogs or people but at least she tolerates their existance.
Hoping this makes sense and it's not a bunch of rambling. I was up until 3am painting and I'm still working on my morning coffee. LOL