By 90 BBY D-4 had served House Serenno for some time, and she accompanied Count Gora, Countess Anya, and their children, Ramil and Jenza, to a celebratory festival held at the planetary capital Carannia. The celebration was designed to allow Outer Rim planets to showcase what they had to offer to the Galactic Republic, and D-4 was keen to point out the opportunity this provided Serenno when Gora began grumbling about the event. In order to avoid a confrontation between the Count and the protocol droid, Anya ordered D-4 to accompany the children around the festival, forcing D-4 to run after them. However, D-4 was unable to keep track of her charges and, following a lightsaber demonstration, she lost them in the crowds. This led to Jenza running into her long-lost brother, the Jedi initiate Dooku.
Years later, in 82 BBY, D-4 attended Anya's funeral on the moon of Mantero along with the rest of the family. There, she witnessed a large protest by the citizens of Serenno against Gora's rule, as well as a clash between Gora and Dooku, who had turned up at the invite of Jenza.
D-4 served Gora for the rest of his reign as count, but during the reign of Ramil, in 42 BBY, Serenno was invaded by Abyssin raiders. In response, Jenza had D-4 smuggled offworld on a Vandyne freighter and taken to Coruscant where he met with Dooku, by now a Jedi Master. Through D-4's holotransmitter, Jenza begged her brother to come to Serenno's aid, and Dooku responded by taking D-4 to the Jedi Council, asking for them to provide help. Unfortunately, as Ramil had not paid levies to the Republic, the Senate had decided that it was none of the Republic's concern and therefore the Jedi refused to accede to Dooku's request.
Nevertheless, Dooku decided to return to Serenno himself. Accompanied by Dooku's old friends, Jedi Master Lene Kostana and her former apprentice Sifo-Dyas, Dooku and D-4 travelled back to the beleaguered planet but, on arrival, they were attacked by Abyssin orb fighters. In the ensuing fight, their ship received multiple hits and Dooku was forced to crash it on the planet's surface. During the crash D-4 was critically damaged; after asking Dooku if they had made it home, she shut down permanently.
D-4 appeared in the audiobook Dooku: Jedi Lost, written by Cavan Scott and published in 2019.