Katherine is a Furisode Girl loyal to Laverre City Gym Leader Valerie. She and another Furisode Girl, Blossom, first appeared spying on Serena and Bonnie when they were looking at Valerie's fashion collection. They thought they would be perfect to participate in a fashion show of Valerie's collection and asked them to come with them. They brought them to Valerie and Katherine introduced them to her.

She reappeared in Fairy-Type Trickery!, following Ash and Valerie's Gym battle.

http://bulbapedia.bulbagarden.net/wiki/Katherine_%28Kalos%29