Wizrain Oukoku Monogatari: Ryuu ga Hanayome

Long ago, the Kingdom of Wizrain was established by a great hero and his precious dragon. But Elna's no hero. She's just the daughter of a nobleman's mistress, adopted into her father's family only to be tormented by her stepmother and stepsister. Or so she thinks...until one day, it all comes flooding back—echoes of her past life as a dragon! Spurred on by memories of soaring through the sky with her hero, she heads for the royal palace. A single look into the eyes of the Young King, Vaide, tells Elna that he is her beloved hero reborn. Only one problem: He doesn't remember her at all!

(Source: Yen Press)