Gerda Idun was born around 2305, one of a pair of twins. Both girls were to be named after their maternal aunts. Unfortunately, one twin died, due to unforeseen complications. The mother, not wishing to offend either of her sisters by naming a dead child after them, named the stillborn infant Helga, and the surviving twin Gerda Idun. The Asmund parents died around 2330, within months of each other, from Belliard's bipolar disease.
Gerda Idun eventually joined the rebellion against the Klingon-Cardassian Alliance. She served as a lieutenant on the Stargazer under Captain Gilaad Ben Zoma. Around 2333, the Stargazer was in a pitched battle against a Klingon bird-of-prey. Casualties from the battle included Andreas Nikolas, Gerda Idun's lover, as well as Phigus Simenon. Shortly thereafter, Gerda Idun crossed over into the primary universe as part of a plan to kidnap USS Stargazer chief engineer Phigus Simenon and bring him to the mirror universe.
While in the primary universe, Gerda Idun encountered alternate versions of several people she knew, including Pug Joseph, Andreas Nikolas, and Gerda and Idun Asmund. She carried on a massive deception to the entire crew of the Stargazer, winning the trust of Captain Jean-Luc Picard and Nikolas. Due to the intervention of both Nikolas and Gerda Asmund, however, Gerda Idun's mission failed, and she returned to the mirror universe, heartbroken over losing Nikolas a second time. (STA novel: Three)