Kelly was born in Los Angeles, California. She is the only child of former Aerosmith guitarist Rick Dufay and the late Maureen Dumont Kelly. She was raised by her mother, who worked various jobs. Kelly and her mother moved to various communities before settling in Chicago by the time Kelly was in junior high school. Kelly's mother Maureen died in 2008, at age 51, from colon cancer. In May 2019, Kelly spoke in an Instagram post about having an abortion, saying "It was the smartest decision I could've made". She has French, Irish and Dutch-Indonesian ancestry.