Born in Meglevo, Imeni Sverdlova, Stepanova started to compete internationally in 1978 at the European Championships in Prague where she finished sixth in her semifinal heat. That year she had a PB of 56.19 seconds in the 400m hurdles. In 1979 she broke the world record for the first time, running 54.78 seconds at the Soviet Spartakiad, defeating previous world record holder Tatyana Zelentsova.