In the 2018–2019 season, Sinitsyna debuted in the ISU Junior Grand Prix series, taking the bronze medal at the 2018 JGP Lithuania.

[3] Sinitsyna then represented Russia in Sakhalin at the first Children of Asia Games, winning the bronze medal behind You Young and Alena Kanysheva.

[4] In March 2019, Sinitsyna represented Russia, alongside countrymates Alexandra Trusova and Anna Shcherbakova, at the World Junior Championships in Zagreb, Croatia after Alena Kostornaia withdrew due to a medical condition.

At the 2019 JGP Italy, Sinitsyna placed first in both the short program and the free skate with new personal best scores and won her first Junior Grand Prix gold medal.

[5] Sinitsyna won the silver medal at the 2020 Winter Youth Olympics behind You Young of South Korea and ahead of Russian teammate Anna Frolova.

[8][9] She was again third after the short program at her second event, the 2021 Internationaux de France, dropping to fourth overall after the free skate with three underrotated triple jumps.