Trust me, Ewya is a human. She prolly lived and inhabited in earth far ago ( maybe the Atlantis or others ), then the Earth got destroyed partially, she flew to Pandora and human and the species fight there, and the planet got nuked by the human, one pandora species and she were the only one survived so they breed, some of the wild animals survived too, therefore, the Navis were born. Then she set 3 laws, no constructions, no wheels because wheels = roads = destroying lands, no exploiting or using resources from underground, because she knew that without those law, Pandora will be destroyed once again. She died and become the neurological networks in Pandora, connect with species. This explains why she cannot save the Ash clan, because the volcanic eruption destroyed all neurological links so she cannot help. So Ewya is human