2021 In June 2021, at age 17, Werro was runner-up in the
800 metres at the Swiss Championships, running 2:02.88 to finish behind champion
Lore Hoffmann. She set new national U18 records over the
400 and 800 metres that year. In July, she went to the
European Under-20 Championships held in
Tallinn, Estonia, where competing against athletes up to two years her senior she won the gold medal for the 800 m.
2022 In February 2022, Werro broke the Swiss U23 indoor 400 m record by 0.84 s with a time of 53.03 seconds in
Magglingen. She next became the national indoor champion over the 800 m, running 2:04.95 also in Magglingen. The same month, Werro also won the Swiss 800 m outdoor title, clocking 2:02.72 in
Zürich. In August, she won the silver medal in the event at the
World U20 Championships held in
Cali, Colombia with an U23 national record of 1:59.53, behind
Roisin Willis for whom it was also the first time she ran sub-two minutes in an 800 m race. The same month, Werro made her debut in the senior championships at the
European Championships in
Munich, where she was eliminated in the heats in 2:06.34.
2023 In early February 2023, the 18-year-old ran a Swiss U23 indoor 800 m record of 2:00.57 in
Val-de-Reuil, just 0.19 s off
Selina Rutz-Büchel's national senior record. This came six days after Werro had lowered Rutz-Büchel's Swiss indoor 600 m record to 1:26.14. In March, at the
European Indoor Championships, held in
Istanbul, she came through two qualifying rounds to reach the final. Werro finished fifth in a time of 2:00.91, 0.06 s away from bronze and beating sixth-placed Lore Hoffmann. In July, Werro won her second national title in the outdoor 800 m with a time of 2:01.70 at the 2023 Swiss Championships in
Bellinzona. She was also the indoor champion over the 800 m for the second year in a row. The following month, she attended the
European U20 Championships, held in
Jerusalem, and won the gold medal in the 800 m for the second time since 2021. In August, Werro set a new 800 metres personal best at the
Diamond League meeting in
Zürich, running 1:59.50. She competed at the
2023 World Athletics Championships in
Budapest in August 2023 finishing 6th in her heat. Shortly after the World Athletics Championships, Werro broke her own national U20 record by running 1:58.13 at the
Galà dei Castelli in
Bellinzona.
2024 She competed in the 800 metres at the
2024 World Athletics Indoor Championships. She won her qualifying heat in a time of 2:01.83. In the semi-final she ran a new indoor personal best time of 2:00.16. She competed in the 800 metres at the
2024 Summer Olympics in
Paris in August 2024. She set a new Swiss national record time of 1:57.76 for the 800 metres in Bellinzona in September 2024.
2025 She was the fastest qualifier for the 800 metres final at the
2025 European Athletics Indoor Championships in
Apeldoorn, Netherlands. She placed fourth in the 800 metres in June 2025 in Stockholm at the
2025 BAUHAUS-galan event, part of the
2025 Diamond League. She ran a 2:34.88 personal best over 1000 metres in Monaco at the
2025 Herculis. She ran a championship record of 1:57.42 to win the gold medal in the 800 metres at the
2025 European Athletics U23 Championships in Bergen, Norway. The following month, she finished runner-up to Keely Hodgkinson over 800m in 1:57.34 at the
2025 Athletissima event in Lausanne and lowered her personal best to 1:56.29 in winning the Swiss Championahips. She ran a 800m personal best 1:55.91 to win the
Diamond League Final in Zurich ahead of
Georgia Hunter Bell on 28 August. In September 2025, she was a finalist in the
women's 800 metres at the
2025 World Athletics Championships in
Tokyo, Japan, placing sixth in a time of 1:56.17.
2026 Werro opened her 2026 indoor season at the Meeting de l’Eure in Val-de-Reuil, a World Athletics Indoor Tour Silver meeting on 1 February, winning over 800m in 1:57.49, taking more than two seconds off her own national indoor record. A few days later she moved to eighth on the world all-time list with 1:57.27 in Belgrade.{{Cite web | url= https://worldathletics.org/competitions/world-athletics-indoor-tour/news/belgrade-indoor-meeting-2026-werro-saraboyukov-steen|date=11 Feb 2026 Chris |last=Broadbent|date=1 Feb 2026 ==Achievements==