"I'm a naiad." She doesn't tell him this because he seems interested - Kriv doesn't seem like he's interested in much of anything about anyone else, at first impression - but because in her mind it's only fair. He told her what she wanted to know, when she asked him a little awkwardly (she knows- there's not really any getting around that, sometimes), and it's fair to tell him that she isn't what she looks like right now.

Then, "Thank you."

He didn't have to answer, he could've just dismissed her in her ignorance.