Lagoa was born in Miami, Florida, in 1967. A Cuban-American, Lagoa is the daughter of parents who fled from Cuba following the Revolution and the assumption of power by Fidel Castro. She grew up in the majority Cuban-American city of Hialeah, Florida. She is bilingual. Lagoa earned a Bachelor of Arts, "cum laude", in 1989 from Florida International University, where she majored in English and was a member of the Phi Kappa Phi honor society. She received her Juris Doctor from Columbia Law School in 1992; while at Columbia, she was an Associate Editor of the "Columbia Law Review".