[2] Her debut on the international stage occurred at the 2016 Junior World Championships in Cheile Grădiștei, Romania, where she secured the 27th position in the individual race.

In the same year, she, alongside Hilde Fenne and Jori Mørkve, clinched the Norwegian championship title in the relay event.

Following a commendable ninth place in the individual race over 15 km at the European Championships in Minsk, Femsteinevik narrowly missed the medal positions in the single-mixed relay, as Endre Strømsheim had to complete three penalty laps after the final shooting.

In the 2019/20 season, Femsteinevik refrained from participating in any international competitions; she returned to the starting line only at the 2021 European Championships but fell significantly short of the top ten in all races.

After somewhat disappointing individual races, she finally achieved her personal best by finishing ninth in the mass start in Le Grand-Bornand in mid-December.