Mya's mother was exiled from the Vale while pregnant with Mya for her part in a romance with Nathaniel Arryn. She grew up in Maidenpool with her mother until the age of six. When her father became aware of her existence, he was already serving as Hand of the King. Regardless of his position, he sent for her and Mya was thereafter raised by Nathaniel himself, as a member of House Arryn.
Mya lived in the Tower of the Hand in the Red Keep up until the War of the False King broke out. She traveled with her stepmother, Alyce Arryn, and half-sister back to the safety of the Eyrie. Her father and cousin, Theon Arryn, eventually returned to the Vale as well. Mya and Theon quickly became close friends, growing up alongside one another.