Von Siebenthal, who starts for Turbach-Bissen, has been taking part in competitions organized by the Fédération Internationale de Ski since 2008 . Until 2013 she mostly competed in junior races. In the 2013/14 season she ran in races in the Alpine Cup , which she finished in fourth place in the overall standings. She ran her first World Cup race in December 2013 in Davos . There she finished 56th over 15 km freestyle. In January 2014 she became Swiss champion in the 10 km pursuit race in Leysin . At the beginning of the 2014/15 season she clinched her first classic World Cup point in Davos with 30th place over 30 km. She finished the Tour de Ski 2015 in 17th place overall. At the Swiss championship in Kandersteg in January 2015, she won the 5 km freestyle. Two weeks later she won bronze in the 10 km freestyle and gold in the 15 km skiathlon race at the U23 World Championships in Almaty 2015 . At the Nordic World Ski Championships in Falun in 2015 , she came 23rd in the 30 km classic mass start race, 22nd place in the skiathlon and sixth place in the 10 km freestyle. At the end of the season she finished third in the U23 World Cup. At the beginning of the 2015/16 season, she took 25th place at the Nordic Opening in Ruka and 15th place at the 2016 Tour de Ski . At the following World Cups, she was three times in the top ten in distance races. In January 2016 she became Swiss champion over 5 km classic in Zweisimmen . At the end of the season she finished 13th in the Ski Tour Canada and came in 18th in the overall World Cup, 12th in the Distance World Cup and second in the U23 classification. The following season she ran to 35th place in the World Cup mini-tour in Lillehammer and eighth place in the Tour de Ski 2016/17 . Her best results at the Nordic World Ski Championships 2017 in Lahti were seventh place with the relay and fourth place in the skiathlon. At the World Cup finals in Québec she came in 25th place in the overall ranking and reached 17th place in the overall World Cup and 13th place in the Distance World Cup. In the 2017/18 season she took 30th place in the Ruka Triple and eighth place in the Tour de Ski 2017/18 . Her best result at the 2018 Winter Olympics in Pyeongchang was sixth in each of the skiathlon and over 10 km freestyle. At the end of the season she came in 31st place at the World Cup finals in Falun and finally reached 17th place in the overall World Cup and 12th place in the Distance World Cup.
In the 2018/19 season, von Siebenthal finished 25th in the Lillehammer Triple, 15th in the Tour de Ski 2018/19 and 40th in the World Cup finals in Québec. At the season highlight, the Nordic World Ski Championships 2019 in Seefeld in Tirol , she came in 18th place in the skiathlon , tenth place with the relay and seventh place in the 30 km mass start race. In March 2019 she won the Engadin Skimarathon . She finished the season in 28th place in the overall World Cup and in 17th place in the Distance World Cup. At the Swiss Championships 2019 in Engelberg , she won the bronze medal in the 5 km freestyle.