She's the avatar of Dana Méadbh, and she's regarded as the Wise One and a prophetess by the villagers.
She appeared in the short story The Edge of the World.
She was older than he had initially thought - her delicate figure had deceived him, so different from the robust build of the other girls in the village.
[...]Lille didn't lower her eyes. They were pale and wildly blue.
In the episode 7, Dolina Kwiatów, of The Hexer TV series, Lille was played by Małgorzata Lipmann.