I think her herding instincts are developing and she's nipping at your ankles to move you along- perfectly normal. And her prey drive is also developing where she wants to chase and bite anything that moves. She's becoming aware of so many drives and instincts, natural behaviors, whatever you want to call it and she has to try them all out. I don't think it's a matter of dominance, she just needs to see what being a gsd is all about- and there's a lot! You might start using NILF, a puppy class, clicker training, etc.