Sometime after her birth, Onielle's Force-sensitivity led her to be trained as a Jedi and she became friends with a fellow youngling, Charlin Plaka. The two became permanently fearful of Iskat Akaris after she accidentally paralyzed her friend Tika with a column during a training exercise. Onielle went on to receive training as a Padawan. In 22 BBY, at the height of the Separatist Crisis, all Jedi were recalled to the Temple on Coruscant, including Onielle and her master. Onielle rejoined Plaka and, after watching her lose a sparring match to Akaris, stepped up to challenge their rival. Despite proving a reasonable challenge to her gifted opponent, Onielle was defeated after Akaris went on an extremely aggressive offensive, ending the match with her training saber at Onielle's throat.
Onielle and her fellow Padawans were soon sent with their masters to Geonosis as part of a Jedi assault team to rescue Knight Obi-Wan Kenobi. Led by Master Klefan Opus, their group infiltrated a tower at the edge of the Petranaki arena. Onielle and several others were disturbed by the behavior of Iskat Akaris when she killed a dozen Geonosians while defending Opus and a fellow Padawan. The group went on to successfully eliminate the Geonosian cannons and guards in the stands, allowing the rest of the assault team to engage the Separatist army in the arena. After withdrawing from the battle by the way they had come, Onielle and the rest of the group returned to Coruscant.
A few weeks later, Onielle, Plaka, and a number of other Padawans were knighted by Master Mace Windu in a mass ceremony. Onielle and Plaka were both unhappy that Akaris was also knighted; all three went on to fight in the Clone Wars.