Couldn't help but notice at one point when Harriet was venting to Nels that, "You go your whole life without meeting one (a Jew) and all of a sudden one shows up right on your doorstep". However, in Season 5, episode 15 "The Craftsman", the main character, Isaac Singerman, was a Jewish craftsman who was the target of prejudice, especially from Harriet and Mr. Larrabee. She most definitely met a Jew in Walnut Grove long before the Cohens.