Daughter of Hounds by Caitlin R. Kiernan

They're known as the Children of the Cuckoo. Stolen from their cribs and raised by ghouls, the changelings serve the creatures who rule the world Below and despise the world Above. Any human contact is strictly forbidden and punishment is swift and severe for those who disobey.

Eight years ago, Emmie Silvey was born on Halloween while a full moon rose in the sky. Raised in Providence by her widower father, she's a strange, yellow-eyed girl, plagued with visions of impossible worlds and fabulous beings. Now her path is about to intersect with one of the changelings, a violent young woman named Soldier who's quickly slipping from the favor of her ghoul masters. Inextricably linked, together they must face the monsters and unearthly forces that have shaped their lives. and threaten their futures.