She sounds like a resilient but suspicious puppy. This is often normal GSD puppy behavior. Before you start teaching her that everybody is her friend, decide on whether that is something you wanted or not. Why did you get this breed? That can be a deciding factor.
Like others said, exposure without interaction is important. I would caution against forcing people on her, not saying that you are, because you may create some nasty reactivity that you won't really want to deal with.
If you need equipment to maintain control of your dog, understand you’re hanging on to your dog’s body because you’ve lost his mind!