Koller first represented Switzerland on the international stage at the 2015 World Mixed Curling Championship, as lead for Yannick Schwaller.

The 2018–19 season was a breakout year for Koller and her team of skip Elena Stern, fourth Briar Hürlimann and second Lisa Gisler.

They missed the playoffs at their next three events, the 2019 Stu Sells Oakville Tankard, the 2019 AMJ Campbell Shorty Jenkins Classic and the inaugural WCT Uiseong International Curling Cup.

They successfully defeated Eve Muirhead in the quarterfinals, Silvana Tirinzoni in the semifinals and Rachel Homan in the final to win the event.

Team Stern surprised many when they upset the defending world champion rink Silvana Tirinzoni in the 2020 Swiss Women's Curling Championship three times and defeated them in the final 6–4.

[12] The team ended their season at the 2021 Champions Cup and 2021 Players' Championship Grand Slam events, which were played in a "curling bubble" in Calgary, Alberta, with no spectators, to avoid the spread of the coronavirus.