In 2017 season, Harnasko made her senior international debut competing at the L.A. Lights. She then competed at the Senior International tournament in Moscow, the Alina Cup where she finished 4th in the all-around behind Israel's Nicol Zelikman. At the 2017 Grand Prix Kiev she finished 10th in the all-around. She finished 5th in the all-around at the 2017 Grand Prix Thiais, she qualified to 3 apparatus finals and won a bronze in clubs. From March 31 – April 2, Harnasko competed at the Grand Prix Marbella finishing 9th in the all-around and qualified 2 event finals, where she won bronze in ribbon. She competed in her first World Cup meet at the Pesaro World Cup where she finished 8th in the all-around behind Israel's Victoria Veinberg Filanovsky, she qualified to 2 apparatus finals finishing 5th in clubs and 7th in hoop. At the 2017 Baku World Cup, she finished 4th in the all-around finals, behind Bulgaria's Neviana Vladinova, and also won a bronze in the ribbon and hoop in the apparatus finals. On May 5–7, Harnasko competed at the 2017 Sofia World Cup again finishing 4th in the all-around, she qualified in 3 apparatus finals and won gold in clubs ahead of hometown girl Neviana Vladinova, bronze in ball and placed 7th in ribbon. On May 19–21, Harnasko along with teammate Katsiaryna Halkina represented the individual seniors for Belarus at the 2017 European Championships, she qualified in all apparatus finals taking bronze in ball, finished 4th in clubs, 5th in ribbon and 7th in hoop. Harnasko's next event was at the 2017 World Challenge Cup Guadalajara where she won bronze in the all-around behind Ekaterina Selezneva, she qualified in 3 apparatus finals: taking silver in hoop, bronze in ball and placed 7th in clubs. On July 7–9, Harnasko finished 16th in the all-around at the 2017 Berlin World Challenge Cup, she qualified in ribbon final. Harnasko competed at the quadrennial held 2017 World Games in Wrocław, Poland from July 20–30, she qualified in 2 apparatus finals finishing 4th in hoop and ball. On August 4–6, Harnasko competed at the 2017 Minsk World Challenge Cup winning silver in the all-around behind Aleksandra Soldatova, she qualified in all 4 apparatus finals taking 2 silver medals in ball and ribbon, a bronze in clubs and finished 7th in hoop. On August 11–13, Harnasko competed at the 2017 Kazan World Challenge Cup finishing 9th in the all-around, she qualified in the hoop final and finished in 5th. On August 30 - September 3, Harnasko and Katsiaryna Halkina represented in the individual competitions for Belarus at the 2017 World Championships in Pesaro, Italy; she qualified in the clubs final and finished in 7th place. Harnasko finished 13th in the all-around final behind Japan's Sumire Kita On September 29-October 1, Harnasko was scheduled to compete at the annual World Club Cup the "Aeon Cup" in Tokyo, Japan; however she withdrew before the start of competition because of injury. In 2018, Harnasko sat out from most competitions recovering from a knee surgery. She competed at Grand PrixMarbella, Spain from October 26–28, where she finished 2nd in all-around behind Ukraine's Vlada Nikolchenko. She qualified to all apparatus finals and placed 5th with hoop, 3rd in ball, 7th in clubs and ribbon. In 2019, Harnasko started the season at L.A. Lights, where she won gold in all-around and clubs, placed 3rd with hoop and ball and 5th with ribbon. She scored 22,200 points with clubs, which is her personal best. Then she competed at Grand Prix Kiev, Ukraine, where she finished 9th in the all-around. She qualified to ball and clubs finals and placed 4th in both. Harnasko's next competition was an international tournament in Corbeil-Essonnes, France, where she won the all-around competition and qualified to all finals. She won three more medals there, bronze with hoop, silver with clubs and gold with ribbon.
