Istomina started in the Eastern Europe Cup for the first time in November 2015 in Werschina Tjoi and finished in 73rd place over 5 km classic, 36th place over 10 km freestyle and 29th place in sprint. In November 2016 she achieved her first podium in the Eastern Europe Cup with second place in the 5 km freestyle in Werschina Tjoi. At the Nordic Junior World Ski Championships 2017 in Soldier Hollow , she won the bronze medal in the 5 km freestyle and the gold medal with the relay. She also achieved 15th place in the sprint and ninth place in the skiathlon . She ran her first World Cup races in December 2017 in Davos , which she finished in 56th place in the sprint and 71st place in the 10 km freestyle. In the same month she was third in the mass start race over 10 km freestyle at the Alpine Cup in St. Ulrich am Pillersee . At the U23 World Championships in Goms in 2018 , she came 26th in the sprint. In February 2018, she was in Syktyvkar Russian U23 champion and won in skiathlon Kononowskaja over 10 km freestyle for the first time in Eastern-Europe Cup. The following month in Oslo she got her first World Cup points with 22nd place in the 30 km mass start race.
In the 2018/19 season, Istomina finished 21st in the Lillehammer Triple, tenth in the Tour de Ski 2018/19 and 33rd in the World Cup finals in Québec . In addition, she achieved her first podium finish in the World Cup with second place in the relay in Beitostølen . At the U23 World Championships in Lahti in 2019 , she won the gold medal in the 10 km freestyle. At the season highlight, the Nordic World Ski Championships 2019 in Seefeld in Tirol , she came in 29th place in the 30 km mass start race and 21st place in the skiathlon . She finished the season in 29th place in the overall World Cup and 23rd in the Distance World Cup.
Russia
