Arngrim left the series at the end of the seventh season. Nellie's resulting departure was explained by having her move with Percival and their twins to New York to run the family business when Percival's father falls ill; the move is made permanent when Percival's father dies. After Nellie's departure became permanent, the Olesons adopted a daughter named Nancy (played by Allison Balson), who bore a striking resemblance to Nellie, although she had a nastier and meaner disposition than Nellie. Nellie—who retained her pleasant personality seen in her later years—returned in the ninth season and met Nancy, who briefly ran away from home when she (mistakenly) believed that her adoptive parents loved Nellie more than her. When Nellie first meets Nancy and sees how she acts, she asks her parents in shock: "I know I was temperamental at her age, but I wasn't "that" bad... was I?" They all start to laugh, then they realize she was as bad.