From Bulbapedia, the community-driven Pokémon encyclopedia.
Luka Carson (Japanese: ルカ・カーソン Luka Carson) is a minor character from the special, Mewtwo Returns and Luna Carson's older sister.
Luka is the bus driver who transports travelers around Mount Quena, since it's impossible to on foot, due to the extreme and unpredictable weather phenomena. After leaving the pick-up point, just missing Ash and his friends, a whirlwind catches the bus and lifts it off the ground, putting Luka and her passengers in danger. Mysteriously, the bus is righted and put back on the road, where it's assumed she made it from there to the arrival point in relative safety.
Luka isn't seen again until the end of the special, where she returned specifically to pick up Cullen Calix at Luna's request. However, between the time of the request and Luka arriving, the pair had changed their minds on Cullen leaving.
In the English dub, Luka is named only in the novel adaptation.