She was an escaped slave, and the experience gave her a strong hatred for the practice. She later became a bounty hunter, and enjoyed capturing slavers with bounties on them. In time, Pilenna became captain of the Gezary.
The Gezary went to the planet Sanctuary to capture incoming ships and collect bounties, preferably on slavers pursuing escaped slaves. However, the Gezary was unable to capture any before they were protected by Sanctuary. Although staying in orbit wasted resources, Pilenna was reluctant to leave and return to her ship's home-port empty-handed. Due to Pilenna's past as a former, escaped slave, the Senites of Sanctuary were willing to talk to her. She also learned to predict the activation of Sanctuary's defenses.
When the USS Enterprise waited in orbit in 2269 while Captain James Kirk, Commander Spock and Doctor Leonard McCoy were trapped on Sanctuary, Pilenna contacted the Enterprise to warn them of an incoming vessel and offered to split a reward if they assisted in its capture, though acting captain Lieutenant commander Montgomery Scott declined. Scott later visited the Gezary and made a deal with Pilenna: Enterprise technicians would repair the Gezary in exchange for contact with the Senites. During the two-week-long arrangement, Pilenna and Scott enjoyed a romantic relationship; she invited him to join her, though Scott refused.
When Kirk, Spock, and McCoy finally did escape Sanctuary in a balloon, the Gezary attacked and attempted to capture them, hoping the unidentified passengers were a valuable bounty. The Gezary worked with a slaving Orion ship during the attack, despite Pilenna's earlier vehement protestations that she wasn't affiliated with them. When Scott asked Pilenna to stop, she broke off their relationship due to his earlier refusal. The Gezary was damaged in the ensuing battle and its orbit decayed into Sanctuary's shield. Scott refused Pilenna's pleas for aid and she and her crew became trapped on Sanctuary. (TOS novel: Sanctuary)