Born in Los Angeles, California, McPhee moved with her parents and sister to the Sherman Oaks neighborhood at age 12. McPhee has been singing since the age of two. Her mother, Patricia Burch McPhee (stage name Peisha Arten), a vocal coach and accomplished cabaret singer, recognized a talent for music in her daughter and decided to train her. Her father, Daniel McPhee, is a television producer and her older sister, Adriana Burch McPhee (born June 30, 1982) is an aspiring producer as well.

McPhee graduated in 2002 from Notre Dame High School. At Notre Dame High School, McPhee was a swimmer and a thespian. She performed in school plays with her elder sister Adriana; both sisters were Homecoming Princess nominees in their senior year. Afterward, McPhee attended Boston Conservatory for three semesters, majoring in musical theater. McPhee left the college due to her manager's suggestion that she try out for television pilots in Los Angeles. In a People news article, it was reported