How does Mrs. Hanrahan's attack on Delphine serve as a symbol of the war itself?

Mrs. Hanrahan's assault on Delphine is defined as an "attack," a reference which, it could be argued, is a representation of the Civil War in miniature. Delphine represents the North with its views of black people as human beings worthy of dignity, and Mrs. Hanrahan the South with its views of black people being, essentially, sub-human property. Here it's important to note that Mrs. Hanrahan (i.e. the narrative) never explains why or how, exactly, she concludes that Delphine has black ancestry.