A 孙女 refers to a granddaughter, the daughter of one's son or daughter.
Topic 1.1: 1.1 Families and Communities in China
孙女 (sūnnǚ) cheat sheet for homework
外孙女 (wàisūnnǚ): A 外孙女 is a granddaughter from one's son or daughter-in-law.
孙子 (sūnzi): A 孙子 refers to a grandson, the son of one's son or daughter.
A 女儿 means daughter, the female child of parents.