Sophie has only appeared in Rise of the Isle of the Lost. She is Yen Sid's mousy human intern. Not surprisingly, she wears a red robe. As the professor's helper she is busy a lot. She grades papers and does research for his experiments, once she even filled a well with water. Luckily she gets nights and weekends off. She is from a place off of the Isle called Eden - it is much greener than the Isle.
Rise of the Isle of the Lost
While Uma is on her hunt for Ursula's shell necklace, she tells Sophie that she has found Yen Sid's big hat. She states that she is willing to barter(trade) the hat for the location of the shattered necklace.