I believe their first encounter already gave her enough clues to prove his human identity. She went as far as to defend Iruma from the suspicion of his father in a way which implied to him that she knew Iruma was a human, but also that she accepts him as one of their own. Because of her penchant for shoujo manga tropes, she pretty much regard humans as similar creatures to demons, albeit with some cultural difference. But the raws hasn't developed their relationship very far, since we're going directly into the music festival