Pre-Chaos: Unknown. And no, Coto will not tell you.
Post-Chaos: She wandered into Resistance HQ and was greeted warmly by Dandi. She somehow knows everyone, but can't remember how.
She is a very humanoid golem. Her maker intended to pass her off as human, and he succeeded - she has hair (fake), natural-looking eyes (lenses), skin-coloured clay and doesn't Talk Like This. She does have a chest cavity, but that's to hold a bottle of blood - this gives her a scent and can fool vampires and werewolves.