Caterina is a sharpshooter from a long line of lawbringers; her great-great-great-great-grandfather formed the settlement of Roca-Lomada in eastern New Mexico, and her father had acted as the town's sheriff since before she was born. Rafael Nievez was a sharpshooter and skilled outdoorsman, both qualities he passed on to his two daughters. Her sister Adelia would go on to become the town's new sheriff, but Caterina had inherited her mother's wanderlust. She joined the New California Republic, who were by then well-established in nearby Southern California. Whilst the rest of the NCR dug in at the Colorado River, Caterina and her fellow Rangers were deployed to Baja California (actually the Mexican peninsula) to patrol and protect the "desert frontiers". They responded to a call from the NCR settlement of Rattletail - only to discover that the "raiders" the settlers had been killing were actually innocent locals.
Caterina had always believed in the NCR's mission, but Chief Hanlon's decision to cover up the settlers' actions struck her as an outrage. She was in the process of being reassigned to the Mojave Wasteland when news of the massacre at Bitter Springs began filtering through the ranks. Caterina subsequently deserted from the NCR in protest, though it cost her almost everything; her entire life was bound up in her service as a Ranger. She took a part-time job with the Mojave Express, couriering packages across the wasteland. However, when a routine delivery took an unexpected turn for the worst, Caterina woke up in a shallow grave just outside Goodsprings. Having been nursed back to health by the townsfolk, she set out to discover the identity of her attackers, and recover the items they had stolen from her.
Since she was a child, Caterina has always been raised to believe in the rule of law. Discovering that the NCR was fallible rocked her entire sense of self, and since resigning her position Caterina has struggled with feelings of shame and anger that prevent her from returning home to New Mexico. This is compounded by the injuries she suffered in Goodsprings, which left her with both visual and coordination issues that affect her ability as a marksman. Despite this, Caterina's calm, easy-going precense continues to serve her well in dealing with the people of New Vegas. Deeply empathetic, she is quick to lend her hand to a worthy cause, and rarely falters in her search for justice - even if it brings her into conflict with other agencies.