Trista Zel served as an officer within Hapan Security around 41 ABY. Being five minutes older than Taryn Zel, her identical twin sister, Trista was also the first cousin of the Queen Mother, Tenel Ka Djo. The appearance of the sisters was nearly indistinguishable from their cousin, Tenel Ka.
Around 20 ABY, Taryn and Trista were born to a male relative of Isolder. Upon reaching adulthood, both Taryn and Trista became officers serving in Hapan Security. Their close familial ties to Tenel Ka made them valuable assets to her. Their relationship to Tenel Ka was kept secret, and they were assigned their own security team to assist them during their missions.
Tenel Ka and Prince Isolder charged Trista and her sister with the mission of locating Ben Skywalker and escorting him back to the Jedi base located on Shedu Maad. However, while en route to meet Isolder at the designated location, the Anakin Solo attacked Isolder's vessel, resulting in the prince's capture. Consequently, the twins brought Ben directly to Tenel Ka to inform her of her father's predicament.
Subsequently, the twins and Ben Skywalker were tasked with the defense of Shedu Maad against an assault by the Anakin Solo. The sisters were horrified by the news that a nanokiller had been unleashed on the Dragon Queen, resulting in the deaths of all those with royal blood aboard. They refused to answer Ben's inquiries regarding whether Tenel Ka and Allana were among the deceased. Shortly thereafter, the twins and Ben uncovered a scheme orchestrated by General Livette to betray the Hapan monarchy through an alliance with the Remnant. Trista volunteered to remain behind to monitor the traitor. She instructed Taryn and Ben to pursue the Remnant forces and their leader, Tahiri Veila.
Later, during the evacuation of the New Jedi Order from the Jedi Academy situated on the planet Ossus, she played a role in the removal of the students and their families before an assault by the Lost Tribe of Sith.