Sonia Vorbarra Vorpatril was a Princess of Barrayar. Her father was Xav Vorbarra, her mother was a Betan woman from the Bureau for Interstellar Trade; she had a sister named Olivia Vorbarra Vorkosigan. She married a Vorpatril who was not in a Countship line and became the mother of Padma Xav Vorpatril.
Sonia and her husband held a family party in their home to celebrate Padma's first birthday. The party was violently interrupted by a death squad, sent by Sonia's uncle Emperor Yuri. Most of the family present were murdered - the survivors were Sonia herself, her son, and her nephew Aral Vorkosigan. Her husband died either at the scene or in the civil war that immediately followed.
Behind the scenes[]
The author has stated on the listserv that Sonia survived the civil war, outlived her husband and parents, and died at some point before the events in Shards of Honor.