She won a bronze medal at the 4 × 5 km relay in the 1997 FIS Nordic World Ski Championships and had her best finish of 16th in two events (5 km + 10 km combined pursuit, 30 km) at those same championships.
Lehtonen's best individual finish at the Winter Olympics was 51st in the 5 km + 10 km combined pursuit at Nagano in 1998.
Her only individual victory was in a 5 km event in Finland in 1997.