Not much is known of Erica's past prior to the start of Gundam SEED. It is known that she aided in the creation of the Earth Alliance's "G Project" (an irony since Erica Simmons is in fact a Coordinator); the creation of the five prototype Mobile Suits: Strike, Aegis, Blitz, Buster and Duel. In secrecy, the information used to build the prototypes was used to develop Orb's own Mobile Suits, the Astray series. When Heliopolis was destroyed, she contacted her old friend, the Professor, to go to Heliopolis and find the Astray prototypes. When she learned one of them, the MBF-P02 Gundam Astray Red Frame, was being piloted by a Natural (Lowe Guele), she had Juri Wu Nien infiltrate his group within the Junk Guild to find out how. She was also willing to allow the group to enter Orb, mostly to gain the data needed to get the M1 Astrays (mass produced version of the Astray prototypes) running.
When the Archangel arrived in Orb, arrangements were made between Chief Representative Uzumi Nara Athha and the ship's commanding officers to have the pilot of the Strike, Kira Yamato, assist in the development of Orb's Astray-type mobile suits. Erica worked alongside Kira in developing an O.S. to allow the M1 Astrays to fight as efficiently as a ZAFT suit.
However, she did know of something else - the fate of the MBF-P01 Gundam Astray Gold Frame, as she spoke to Rondo Gina Sahaku and expressed her dismay over him wanting to destroy the Giga Float the Junk Guild was working on.
Erica was among the Orb personnel evacuated into space aboard the Kusanagi. During the Battle of Jachin Due, she gives an overview of ZAFT's superweapon known as GENESIS and oversees the assembly of the Strike Rouge in space.
Gundam SEED Destiny
As ZAFT's Operation Fury is ongoing, it is Erica who presented Cagalli with Lord Uzumi's "last will": the ORB-01 Akatsuki Gundam.