Pokémon: DP Sinnoh League Victors: Narissa

Narissa is a Pokemon trainer that the gang meets in episode 641. She is initially very incompetent, but Brock teaches her to be better.

Pokemon Diamond & Pearl: Dawn

Dawn began her Pokémon journey with an overconfident Piplup. She wasn't able to gain his trust at first, but after rescuing him from a swarm of Ariados, the two became friends. Unlike May, she knew from the beginning that she wanted to follow in her mother's footsteps and be a Coordinator. After meeting Ash and Brock, she decided to travel with them, as their experience would likely be helpful to her.