Battling with Elegance and a Big Smile!

While training for their next Showcase, Serena ends up going harsh on Fennekin and Pancham when training doesn't go right, still torn from the loss in her first. Feeling down, she leaves Ash and Bonnie for a while for some alone time. As she walks through the city, she meets a girl who randomly approaches her to talk, and they end up going shopping together before finally having a practice battle against her Delphox and Aromatisse. The question is, who is this mysterious girl?