Sophie has apparently been working in the idol industry since she was very young. She is also very popular at her school, and admired by many of the students. When she eats a Red Flash (pickled plum), her personality - likewise with her appearance - changes. Her public personality is cool and on top of things, while her other personality (aka 'Fancy Mode') is extremely disoriented and directionless. It is also hinted that she has low blood pressure. While she is in her Fancy Mode, she says "Pshu~" a lot. In Fancy Mode, she is quite naive and oblivious to what's around her, but since forming her friendship with Lala and Mirei, she has been working on improving herself.
(Source: PriPara Wiki)