De Santo was born on Tyrador IX as the daughter of indentured workers and was forced to work in the world's spas and resorts to pay off a debt to a Confederate financial institution. Not wanting to remain in such an occupation, she enlisted in the Confederate Armed Forces on her eighteenth birthday in a bid to change her situation.
She became a marine and while a good soldier, de Santo possessed a truculent mouth and rebellious streak, one which continued in Dominion section under Arcturus Mengsk, whom she considered arrogant and selfish. However, the two of them got on well, de Santo showing immense loyalty to her superior officer. Her first combat experience came six months after her assignment in August, 2480, a period when she and the rest of her unit were supposed to be on leave. With the 33rd Ground Assault Division, Kel-Morian miners were stripped of their claims to the world of Sonyan after a battle in Turanga Canyon, de Santo succesfully flanking them alongside Mengsk and fellow section member Chun Leung.
Over the next five years, de Santo continued to serve in the unit, visiting worlds such as Parragos and Pho-Rekh. In 2485, one of these worlds was Onuru Sigma, an attempt to evict Kel-Morian workers resulting in the Battle of Noranda Glacier. Although she sufferred a wound to her arm along with any damage incurred by the use of stimulants, De Santo survived the battle and went on to fight for the Confederacy in the Guild Wars. When Mengsk left the military to become a prospector, she invested what money she'd saved in his business and became a skilled prospector as well. Eventually she and Mengsk struck it rich at Pike's Peak.
Mengsk skipped the party when he received a desperate appeal from Umoja.