Sal is the Mother’s daughter and Josie’s sister who died of disease at a young age. It was a painful event for everyone, and this prompted the mother to have Mr. Capaldi create a replica of Sal as a sort of grieving doll (which Miss Helen happens to see through a window), although the doll was apparently discarded soon after. The experience with Sal is what prompts the Mother to hire Mr. Capaldi to create a “portrait” of Josie (which is not really a portrait, but in fact a lifelike replica that will be filled with Klara’s consciousness if Josie ever dies).