Weng, who competes for the Nes Ski, first appeared at the European Youth Olympic Winter Festival 2013 in Predeal . There she won the bronze medal with the relay. In the following year she won the bronze medal with the relay and the silver medal in the sprint at the Nordic Junior World Ski Championships 2014 in Fiemme Valley . In addition, she achieved 21st place over 5 km classic and fourth place in the skiathlon . In February 2015 she won the gold medal with the relay at the Nordic Junior World Ski Championships 2015 in Almaty . In the same month she was Norwegian junior champion over 5 km, over 15 km and in the sprint. The following month she made her debut in Drammen in the cross-country skiing world cup and finished 52nd in the sprint. At the Nordic Junior World Ski Championships 2016 in Rasnov , she won the silver medal in the sprint, over 5 km classic and with the relay. In February 2016, as in the previous year, she became Norwegian junior sprint champion. At the Norwegian Championships in 2015 and 2016, she and Tiril Udnes Weng took third place in the team sprint. At the beginning of the 2016/17 season, she got her first World Cup points at the Nordic Opening in Lillehammer , which she finished in 39th place, with 22nd place over 5 km freestyle. At the following Scandinavian Cup in Lillehammer, she achieved third place over 5 km freestyle and second place in the sprint. At the U23 World Championships in 2017 in Soldier Hollow , she won the gold medal in the skiathlon. She was also sixth in the sprint and fourth in the 10 km freestyle. At the end of the season she reached third place in the overall ranking of the Scandinavian Cup. In 2017 and 2018 she became Norwegian champion in the team sprint together with Tiril Udnes Weng. In the 2017/18 season she finished in the top ten six times in the Scandinavian Cup, including first place in the sprint in Piteå and thus achieved second place in the overall ranking of the Scandinavian Cup. At the U23 World Championships in Goms in 2018 , she finished 13th in the skiathlon.
In the 2018/19 season, Weng finished 36th in the Lillehammer Triple and 32nd in the sprint at the 2019 Nordic World Ski Championships in Seefeld in Tyrol . In addition, she came under the top ten three times in the sprint and finally reached 35th place in the overall World Cup and 28th place in the Sprint World Cup. At the end of January 2019 she became Norwegian champion in the sprint and second in the relay in Meråker .
Weng is the twin sister of Tiril Udnes Weng and the cousin of Heidi Weng . who are also cross-country skiers.