Okay, I apologize to the Petsmart Trainers we have on this list, right now, as this is not aimed at all Petsmart Trainers, but MOST do not have the knowledge/training experience to deal with this type of behavior. Their great for puppy socialization, but they are not behaviorists, and most dogs need more than a puppy class.
Has your mom been in contact with the breeder of her dog? If its a good breeder, they should know ways that could help, as well as trainers they would recommend. At the very least they need to be notified of what has happened.
Your mom needs to decide how dedicated she is to this dog and working on this problem. No matter what training happens it will take time/months maybe even years for this to be under control, but keep in mind this behavior probably will not go away, but it can become managed. How far are you from Raleigh, NC? I can pm you the name of a person who has MANY years of experience with evaluating and training problems. She may even know someone closer to you if she's not available.
Yes, your mom and you can probably see a lot of things that should have been done differently, but now you need to be proactive. You can check out Obedience Trainers in your area and ask them if they know anyone they would recommend. Given that this is a German Shepherd, you could possibly call your local police department and ask them if they have a canine Officer who you could get in contact with for help/insight.
Overall this situation puts your mom in a very unfortunate circumstance, but it is also a natural thing for this breed to be protective. It is very important for any German Shepherd Owner, or any Guarding Breed of dog, to have training to control the behavior.