The term FAMILY GIRL can be broken down into two crossword solutions: SIS (3 letters) and NIECE (5 letters). SIS is an abbreviation for the word 'SISTER', which is a female family member who shares the same parents as another person. A NIECE is a female family member who is the daughter of one's brother or SISTER. Both terms refer to a female family member, making them both valid solutions for the term FAMILY GIRL.