The Fire And The Crystal - book 1

Mya is Sensi Wu's adopted daughter. He adopted her when she was a baby. She is 7 years older than Lloyd. She is the elemental master of crystal. Her father treated her differently once Moro was on the team; once he ran away her father went out for his "replacement". When Cole was made team leader she looked at her dad and said
"If you don't start seeing me as a ninja I will run away like Moro did, but for a different reason"
Her father just went on with his mission and soon Jay, Zane and Kai were all made ninjas and she was forgotten. She made friends with Nya. She eventually runs away, but keeps in contact with Nya. She is 17 years old and working in Ninjago City at the library. She gets a random call from Nya telling her that her cousin unleashed the serpentine so be careful. Mya hasn't used her powers since she ran away.