Palpatine's second sister was one of at least two female children of Naboo aristocrat and head of House Palpatine Cosinga Palpatine and his wife, and sister to Palpatine, future Dark Lord of the Sith as Darth Sidious, Senator of Naboo, Supreme Chancellor of the Republic, and Emperor of the galaxy.
Palpatine's relationship with his second sister was—as with all his siblings—cold. She and the others considered him an interloper—in turn, he considered them "well-behaved" subservients and held them in contempt.
In 65 BBY, Palpatine's sister traveled to Chandrila in the Palpatine family yacht with her father, mother, siblings and bodyguards, in order to forcefully recover their eldest brother from Chandrila. After the starship left the planet, Palpatine slaughtered his family and the bodyguards using the dark side of the the Force, leaving no survivors.
Palpatine remembered the lifeless forms of his siblings slumped on the starship floor every time his Sith master, Darth Plagueis, urged him to recall the murders in vivid detail as part of his training in the dark side.
- Darth Plagueis (First appearance)