[2] Mainardi made her international debut at the 2021 Junior Pan American Championships and won a bronze medal with the Argentine team behind the United States and Brazil.

[4] Mainardi competed at the 2022 South American Youth Games, winning gold in the all-around, vault, and floor exercise.

[5] At the 2022 Junior Pan American Championships, she won a bronze medal with the Argentine team.

[8] She finished her 2022 season at the Top Gym Tournament in Charleroi, Belgium, winning bronze medals on the vault and floor exercise and placing seventh all-around.

[9] Mainardi was selected to compete at the 2023 Junior World Championships in Antalya, Turkey alongside Emilia Acosta and Isabella Ajalla, and the team finished in fifth place.