[Karin]

Long shot ...if she is around 18 months of age, this is the "social maturity" age for a dog of this breeding. Females can be very dominate, most always alpa dogs. Contact a trainer or find a trainer who would be willing to foster her during training.

The real world...like others have said, not all can be saved. In no way did you fail. This could be in the dogs personna..ingrained for reasons unknown. HS's do have to euthanize aggressive/dangerous dogs. They can and will be a libility.
I had to do the same when I worked at a shelter, a litter of 6 Chow puppies from a pet store. The store paid top dollar for them and tried to work it out but the pups were growing up behind the scenes, they were so vicious Chow rescue did not want them and recommended euthanasia.
Sometimes one never knows what is in a dog or any other mammals make up to make them snap.
Good luck, and remember you did not fail in anyway.