Marko-Varga was an early prospect, winning two individual freestyle titles at the 1998 Swedish Swimming Championships at the age of 13.

She won all the five titles she contested for in the Swedish Youth Championships the same summer, although she was one year younger than the others in her age group.

At the Swedish Youth Short Course Championships she won six individual titles and two relay medals, still being one year younger.

She won a bronze medal in the 200-metre freestyle event at the 2000 European Junior Swimming Championships, behind Irina Oufimtseva and Éva Risztov.

At the Athens 2004 Olympic Games she swam in the 4 × 200 m freestyle relay (with Josefin Lillhage, Malin Svahnström and Lotta Wänberg), finishing 8th in the final.