Shackell was born November 13, 2006 in Carmel, Indiana. Graduating in June, 2025, she attended
Carmel High School and swam for their exceptional swimming program under Coach Chris Plumb. Shackell won the 100-yard butterfly event at the Indiana High School Athletic Association annual championship meet all four years of her High School participation. Considered by a few sports historians to be the greatest team ever assembled, by 2023, the Carmel High girls' team had won 37 consecutive Indiana State championships. In addition to Alex, three other Carmel swimmers Kayla Han, Lynsey Bowen and Molly Sweeny won medals in international competition in 2023. She set a state record of 51.71 in the 100-yard butterfly at the 2022 Girls Swimming and Diving State Tournament at Indiana University in Indianapolis. == International competition highlights ==