A prolific indie artist, she is known for her numerous live and studio collaborations with Pan Sonic, Throbbing Gristle, múm, Ben Frost, Ilpo Väisänen's [url=https://www.discogs.com/artist/69987]Angel[/url], Jóhann Jóhannsson, Animal Collective, [a=Sunn O)))], [url=https://www.discogs.com/artist/630881]Robert Aiki Aubrey Lowe[/url], Hauschka, the duo of BJ Nilsen & Stilluppsteypa, The Knife, and many others.

In 2007, Hildur released her debut solo album, Mount A under the Lost in Hildurness alias. She worked on it alone, playing and recording cello, viola, piano, zither, vibraphone and gamelan. A follow-up Without Sinking was released in 2009 by British label [l=Touch], as well as her next works Leyfðu Ljósinu (a concert album capturing live performance without any editing or post-production) and her most recent album Saman, which melts the sounds of her voice and cello together to form a single instrument.

Guðnadóttir is also a vocal performer, and once she arranged a choir for Throbbing Gristle performances in Austria and UK. As a composer, she wrote a score for the play Sumardagur performed at Iceland's National Theatre, as well as the Danish film Kapringen.