Sonia is the granddaughter of the professor in the game. She’s training to become a professor of Pokemon herself. Her name is one of the few Pokemon characters where it’s the same in Japanese and English.
She doesn’t do much in the game, I will admit her fandom is more based on her looks than anything.
But she was often there to support Hop and yourself.
But in her findings for ancient Pokemon, her research makes her become a Pokemon professor.