Kristoffersen competed internationally for the first time in an FIS race in March 2006. After she was able to achieve several placements among the top ten and once the podium in third in these lower class competitions, she was nominated in February and March 2007 first for the European Youth Olympic Winter Festival and then for the Nordic Junior World Championship. Both times she won the silver medal over 5 kilometers, and she also triumphed at the Youth Festival on the 10-kilometer route. After further good FIS races, she was nominated for the first time for the cross-country skiing world cup in Beitostølen in November 2007 . There she achieved a 19th place straight away, with the relay she reached seventh place. Shortly thereafter, she won her first FIS race in December and won silver at the Norwegian Championship in February 2008 in the pursuit behind Marit Bjørgen . The season ended for Kristoffersen with further World Cup points, including a twelfth place over 10 kilometers and the junior world championship title with the relay.
At the beginning of the 2008/09 season Kristoffersen won her first World Cup victory with the relay in Gällivare . In February 2009 she again won the gold medal with the relay at the Nordic Junior World Ski Championships . In the same month she finished 12th in the 30 km mass start race at the Nordic World Ski Championships in Liberec , eighth place in the sprint and fourth place with the relay. At the end of the season she achieved her first World Cup podium in an individual race in Lahti with third place over 10 km freestyle. At the 2009 World Cup finals in Falun , she finished ninth in the overall ranking. After a mediocre start to the 2009/10 season, she finished the 2009/10 Tour de Ski in tenth place overall. In her first Olympic participation in Vancouver in 2010 , she came in 48th place over 10 km freestyle and 20th place in the 30 km mass start race. In March 2010 she won the relay in Lahti. In the overall World Cup ranking, she finished 12th. The following season she came in seventh place overall at the Tour de Ski 2010/11 . He reached third place in the 10 km pursuit race and in the mountain stage. At the Nordic World Ski Championships 2011 in Oslo , she achieved 15th place in the 15 km pursuit race. She finished the season in 13th place overall.
At the beginning of the 2011/12 season she came ninth at the Nordic Opening in Kuusamo . At the Tour de Ski 2011/12 , she reached fifth place in the overall standings. This was followed by two third places in the 10 km mass start race in Rybinsk and in the relay in Nové Město . At the World Cup finals, she took seventh place. She finished the season in sixth place in the overall World Cup ranking and fifth in the distance ranking. In the 2013/14 season she started in the Scandinavian Cup. She achieved three podium positions including one victory. It took third place in the overall ranking. In April 2016 she became Norwegian champion in the team sprint together with Kathrine Harsem in Beitostølen . In the 2016/17 season she achieved 28th place in the World Cup mini tour in Lillehammer and 29th place in the World Cup final in Québec and reached 53rd place in the overall World Cup. At the Norwegian Championships in 2017, she was champion with the relay and third together with Kathrine Harsem in the team sprint. The following year she won again with the relay.
Norway
Gällivare
Lahti
