Born and raised in Kansas City, Missouri by parents Neil and Shelley Kelly, Katie, attended and played for St. Teresa's Academy. She earned many accolades while playing for the Stars, helping them to state titles in 2002, 2003 and 2005. During her time with the squad, she scored 32 goals and served 59 assists. During her freshman year, she was an all-state second-team selection and first-team all-district selection. She was named first-team all-state, all-conference, all-district and all-metro during her final three years. During her senior year, she was named Missouri State Player of the Year, Western Region Player of the Year and was a high school All-America selection.