In 1998, Erna joined Children of Bodom on their first European tour, temporarily replacing keyboardist Janne Wirman. In the same year, Erna sang soprano on the album Fallen Angel's Symphony for the German band Ancient Ceremony. In 1999, she played keyboard for Sinergy during their live gigs. Erna was also keyboardist for the Finnish group Grain, until their split in 2001. In 2001 and 2002, she played synthesizer in Markku Klami's Meditation (op. 10/1) and Hymn For Christmas.
In 2006, Erna joined the Finnish "gravedigger metal" band Deathlike Silence, replacing former keyboardist Mr. Rigor Mortis.