Atom Girl's existence was nothing but myth to the second wave of Legion of Super-Heroes. Her very existence was in doubt until Brainiac 5 enlisted her aid to stop Elysion of Terror Firma from destroying the United Planets' headquarters on Earth. She claims to have been exploring Brainy's microverse and simply lost track of time. When Invisible Kid had used "the Shrinking Violet" as excuse when confronted for his betrayal to Cosmic Boy, Invisible Kid and Atom Girl agreed to continue the ruse, as she prefers her presence on the team a mystery.
Later, on a mission on Lallor, she battled E.R.G.-1 with Shadow Lass and Timber Wolf. Atom Girl convinced E.R.G.-1 to redeem himself, as it was revealed that he had been manipulated. Atom Girl has expressed interest in dating him.