When Laura Ingalls Wilder wrote The Little House series of books, she changed the names of a few of the different characters that she was detailing in a way that she thought was in a negative light. One of those characters was that of Nellie Oleson.
In On The Banks of Plum Creek, the readers are introduced to Nellie Oleson, which was actually the combination of three different girls. Those girls were Nellie Owens, which is where the name Nellie Oleson comes from, well as Genevieve Masters and Stella Gilbert.
Genevieve Masters died before On The Banks of Plum Creek was published. But both Nellie Owens and Stella Gilbert were alive when On the Banks of Plum Creek was published.
There’s no confirmation that either woman knew they were based on the character of Nellie Oleson. However one of the children of Nellie Owens did acknowledge that Nellie Oleson was based on Nellie Owens.