[1] From Varaždin, Koščak secured five personal bests in winning the 2022 European Athletics U18 Championships Heptathlon event, held in Jerusalem in July 2022.

[3] In January 2023 Koscak cleared 1.90m in the high jump to break the Croatian indoor U18 record held previously by Blanka Vlašić.

[7][8] In May 2023 she was awarded “rookie of the meet” when she finished ninth overall competing with senior women at the Hypo-Meeting in Gotzis.

[12] She won gold in the heptathlon at the 2024 World Athletics U20 Championships in Lima, Peru in August 2024.

[13] In February 2025, she managed 4478 in the heptathlon ro to break her own Croatian record at the World Athletics Combined Events Tour Silver meeting in Tallinn, Estonia.