The sibling of Talia, a Nightsister, was a Dathomirian Zabrak woman originating from the world of Dathomir, and a member of Mother Talzin's coven. During the Nightsister initiation ritual involving the Sleeper, this sister was overcome with terror upon seeing the ancient being, and was pulled into the water where the Sleeper resided. Talia was helpless as she witnessed what happened to her sister. Later, in 19 BBY, when Asajj Ventress, a Force-Sensitive Outcast and Nightsister, started teaching the Jedi Quinlan Vos about the dark side, she recounted the twin's experience with the Sleeper.
The 2015 book Dark Disciple, authored by Christie Golden, included a reference to Talia's twin.