Born and raised in Los Angeles, Courtnall began playing soccer with an AYSO team at age five and also grew up running track.
She attended Oaks Christian School in Westlake Village, which she helped lead to the state track championship in 2019.
In her senior season in 2024, she contributed to 11 clean sheets in 23 games and captained USC to the Big Ten Conference regular-season title and the quarterfinals of the NCAA tournament.
She appeared in all 7 games (3 starts) and scored 2 goals at the 2022 CONCACAF Women's U-20 Championship as Canada came away with the bronze medal.
[1][8] Courtnall's sister, Ally, is a model and former UCLA two-sport athlete in soccer and track, and her brother, Lawton, played college ice hockey at Western Michigan.