This against her own culture.
Yes -- and no. That didn't reflect "the existing left wing views of that era." Rather, it was the attitude of well-off Southern Whites to the PWT of the era. And they didn't think of class-based condescension as an attack on their own culture.
Left-wing attitudes were more complicated back. Of course there were all those images of violence in the South on the news, and of course liberals and radicals were on the side of integration, but lefties were singing all kinds of folk songs about working people, so their views were more nuanced back then.
If I may interject, the incestual culture of Mayella and Bob Ewell was very far removed from the culture of Scout, Jem, Atticus and Dill, and even Calpurnia.