Heir to the Sky - Amanda Sun

As heir to a kingdom of floating continents, Kali has spent her life bound by limits: by her duties as a member of the royal family, by a forced betrothal to the son of a nobleman, and by the edge of the only world she's ever knowna small island hovering above a monster-ridden earth, long since uninhabited by humans. She is the Eternal Flame of Hope for what's left of mankind, the wick and the wax burning in service for her people, and for their revered Phoenix, whose magic keeps them aloft.

When Kali falls off the edge of her kingdom and miraculously survives, she is shocked to discover there are still humans on the earth. Determined to get home, Kali entrusts a rugged monster-hunter named Griffin to guide her across a world overrun by chimera, storm dragons, basilisks and other terrifying creatures. But the more time she spends on earth, the more dark truths she begins to uncover about her home in the sky, and the more resolute she is to start burning for herself."