Our dog is afraid of us, what can we do?

I am almost in tears as I am writing this but I am desperately looking for some help with regards to my Boston Terrier. We have had her for eight months and she is now one year old. The problem we are having is that the dog is petrified of human contact.
We got her from a breeder when she was five months old. The breeder stated that the first owner returned her to them because they could not bond with the dog. Most dogs run up to greet their owner when they return home, well ours runs away from us.
She spends most of her time within the home avoiding her family. We have had her checked out by the vet who thinks that she may have suffered some traumatic event before we got her which has damaged her confidence and that she may also be naturally timid.
We also have spent some time with a behaviourist who shares the same opinion however nothing they have suggested has helped her gain confidence. She attends dog training class an although she does show some interest in some of the other dogs any interaction with people results in extreme fearfulness (trembling, shaking etc).
She is so afraid of her own family that when anyone puts the lead on her before going for a walk quite often results in her losing control of her bowels and she poops on the floor.
Is there anything we can do to help her?
We all love her very much and I always said I would never return her to the breeder but the dog is so afraid of us and seems to be so unhappy that I often wonder if I am doing the wrong thing by keeping her here.
I am afraid that one day her little heart will give out due to her state of mind. Any help by anyone would be greatly appreciated.
Paul Daly, by email

What a very sad story. It does sound like something catastrophic has gone wrong with this little dog's early socialisation. Is there anyone who has overcome such a problem? Any hints you can pass on. I'm emailing to ask for locality as I'm guessing some local assistance may be needed. My instincts are to discover if this was a dog that ended up bonding with another dog not people, perhaps another small dog. Behaviourists, would the presence of another dog that is confident and friendly with people help bridge the gap or just make things worse?
Beverley Cuddy, Editor