Kilgore was born in Humble, Texas and raised by her adoptive parents in Oregon. She started singing and performing at an early age. At the age of 9, she began singing the National Anthem for sporting events in the Portland area, including the Trailblazers, Winterhawks, and Portland Beavers. She took part in several pageants and won the 2012 National American Miss Oregon Pre-Teen Title as well as the National American Miss National Spokesmodel competition. In 2015, she won the Miss Oregon's Outstanding Teen competition.
Hailey attended Clackamas High School for two years, where she performed in a number of plays. She was Tiger Lily in "Peter Pan" and Fruma Sarah in "Fiddler on the Roof," among others. During those 2 years, she also took part in the August Wilson Monologue Competition. In 2015, she took second place in the Portland competition and performed in the national competition in New York. In the Fall of 2015, Hailey transferred to the Clackamas Web Academy, after taking the role of Rebecca Gibbs in Portland Center Stage's production of "Our Town." Later that Fall, she also performed in the ensemble of PCS's production of "Ain't Misbehavin.'"
Hailey graduated a year early and enrolled at the American Musical and Dramatic Academy in New York in the Fall of 2016. She was cast as Ti Moune in the Broadway revival of "Once on this Island" which opened December 3rd, 2017. Hailey received a number of award nominations for her performance, including nominations for a Chita Rivera Award for Outstanding Female Dancer, Outer Critics Circle Award for Outstanding Actress in a Musical, Drama League Award for Distinguished Performance, and a Tony nomination for Best Actress in a Musical. She received a Theatre World Award for her performance, and won both the Broadway.com Audience Award for Favorite Leading Actress in a Musical, and the Broadwayworld.com Fan Choice Award for Best Leading Actress in a Musical.