What a beautiful girl.
To me she looks mixed, with what I'm not too sure but I would say a Kelpie. I don't know if USA have Kelpie's, they are a very popular breed in Australia due to their exceptional herding/working abilities. I once fostered a german shepherd cross kelpie girl for a week and your girl reminds me of her.
Having said this, their are black pedigree GSDs, however your girl looks quite fine boned which made me think of the Kelpie mix.
Also, if she is only 1 and 1/2 years old then she wouldn't have come into her full coat yet and her colour still may change.