Katherine Hailfrey (Goes by Kat) is a Pokemon trainer beginning her journey along with Edd Mikey and David. At first, she challenged Mikey to a duel with her Snivy, but her Plant Pokemon was easily beaten by Mikey's Charmander, a Fire type. She then decided to join the group, and the three have remained friends ever since. Her ultimate goal is to prove that Pokemon with a heavy disadvantage can still win against more powerful, opposing Pokemon.
So far, it is not revealed that Katherine has any siblings or family outside her direct bloodline. However, it has not yet been asked this, either, so the question could lead to the answer.
Snivy is Kat's main Pokemon. It is a Plant type that lost it's first battle, but has gotten more powerful since. Snivy is a shy Pokemon, so Kat has trouble getting it out of it's Pokeball outside of Battle.
Kat's Pikachu is a wild Pokemon she managed to catch with the help of Mikey's Charmander. It has since remained loyal to Kat, trying to learn all it can from her and her friends.