 In recent seasons Hartelius took part as soprano soloist in John Eliot Gardiner's Bach Cantata Pilgrimage (2000), and debuted as Marzelline in "Fidelio" at the Bavarian State Opera.She was highly praised for her appearance in Nikolaus Harnoncourt's realisation of Schubert's rarely played opera "Alfonso und Estrella" at the Zürich Opera and performed at the Salzburg Festival 2000 in various concerts alongside the Vienna Philharmonic with Wolfgang Sawallisch and Charles Mackerras conducting.In the Salzburg Festival 2001 she sang Adele in the new production of "Die Fledermaus" and concerts with the Mozarteum Orchestra conducted by Ivor Bolton.