Well, 5oaK explicitly says her mother was an amazon, but even without that, she'd pretty much have to be an amazon through her mother, because if she were an amazon through her father, a) it seems beyond doubtful the Bana would consider her one of them in the first place, and b) there'd be no way whatsoever to confirm her ethnicity even if they wanted to. The Bana have been breeding with humans for thirty centuries - there's no possibility that there's anything distinct enough about them genetically to be verifiable. The only way they could be *sure* Grace is a Bana is a mitochondrial DNA test. Which of course requires her to be an amazon through her maternal line.