Sophia is a talented child actress, director, and producer who has made the Turner parents very rich and happy. She exists in a timeline without Timmy. Instead, the Turners had a daughter who brought them great success.
She looks exactly like Timmy, but with long hair, and no pink hat. She wears a pink dress and has stud earrings.
Sophia was mentioned in the episode It's A Wishful Life. Timmy Turner, feeling unappreciated, wishes for an world without him. He is wished into an alternate reality where his family lives in a mansion in place of their normal home, and have a daughter instead of Timmy. Mr. and Mrs. Turner are overheard talking about their daughter Sophia, who is winning an award for acting, directing, and producing. Sophia's success has made the Turner family very rich.
After Timmy is wished back into existence and returns to his normal life, Sophia is unwished or perhaps erased from existence entirely. She is not referenced in the show again.