When she was in the fourth grade of elementary school, she took up cross-country skiing together with her twin sister Vita.

Valja managed to qualify for 2006 Winter Olympics, where she took part only in individual race, finishing 46th.

First individual podium Valja celebrated on 4 February 2011, in Presque Isle, United States, in sprint.

On 15 December 2013, Valja won a pursuit race in Annecy, France, which was her first individual World Cup victory.

Together with Juliya Dzhyma, Vita Semerenko and Olena Pidhrushna she won the gold medal in the Women's relay at the 2014 Winter Olympics, in Sochi, Russia.

Later she accused coaches of ignoring her results and including not so successful at the Games Iryna Varvynets and Anastasiya Merkushyna in the relay team.

Her sister Vita Semerenko later told in an interview that Valja cried for hours after discovering that she wouldn't participate in the relay.