A frequent collaborator of Arjen Anthony Lucassen, she portrayed main characters in the albums Into the Electric Castle, 01011001 and The Theater Equation by his project Ayreon.

Van Giersbergen has also prominently collaborated with Devin Townsend on many of his albums, Within Temptation, Anathema, Lawn, Farmer Boys, Napalm Death, Moonspell, Novembers Doom, Globus, Giant Squid, and many other artists and projects.

In 1992, she founded the duo "Bad Breath" with guitarist and singer Deniz Cagdas (Spencer Edgards), with music predominantly based on blues, jazz, folk and funk.

In 2006, she appeared on the album 2006 Rubicon from Asia band members' John Wetton and Geoffrey Downes on the tracks "To Catch a Thief" and "Tears of Joy".

[5] In June 2006, the epic rock band Globus released the album Epicon, which included Van Giersbergen's vocal and writing contributions.

Van Giersbergen co-wrote the lyrics for "Mighty Rivers Run", and sang lead vocal on the track as well as dueting with Christine Navarro on the seminal "Diem Ex Dei".

On 5 June 2007 it was announced that Van Giersbergen would be leaving The Gathering in August 2007 to focus on a new project, Agua de Annique,[6] and to spend more time with her family.

[11] Van Giersbergen also features on a track in the orchestral re-interpretations album from English progressive rock band Anathema, Falling Deeper, released on 5 September 2011.

[12] On 22 April 2014, Arjen Anthony Lucassen revealed that his next project would be a collaboration with Van Giersbergen, their third work together after the Ayreon albums Into the Electric Castle and 01011001.

In 2018 she performed on "Amongst Stars" from Finnish Heavy Metal band Amorphis' album Queen of Time, including appearing on the official music video.

[16] She also performed in two concerts alongside Residentie Orkest The Hague covering songs from Van Giersbergen's whole career, later released in the live album Symphonized in October.