Amber appears at first at Mount Highpoint. She tells you about a few weird guys. After that, she appears again and battles with you Team Solar and Lunar.
After this, She appears as the leader of Highpoint City's Gym. This gym is the fifth to be challenged by the player. Trainers who defeat Amber will receive the Blast Badge, along with TM102 (Solar Claw).
Afer earning the Blast Badge, she comes out of her gym and gives you the Core Stone to protect.