 After debuting at the Ludwigsburg Festival (1990) and Schwetzingen Festival (1991), Hartelius appeared for the first time at the Salzburg Festival in 1992 as Barbarina in "The Marriage of Figaro".Upon returning to the Salzburg Festival in 1996, she began her association with conductor Franz Welser-Möst in performances of Bach's "Mass in B Minor" (BWV 232) and "St Matthew Passion" (BWV 244) with the Camerata Accademica and in 1997, she sang Blondchen in Mozart's "Die Entführung aus dem Serail" conducted by Marc Minkowski.Her operatic repertoire continues to expand with performances of Donizetti's "L'elisir d'amore" and "Don Pasquale", Mozart's "The Magic Flute" and "The Marriage of Figaro" and Strauss' "Ariadne auf Naxos".