What characteristics of modernism are in "A Rose for Emily"?
Tension between the modern and the old, specifically, the Old South, pervades "A Rose for Emily" from beginning to end.
From the very first scene in the story, Miss Emily's house, which once was on an upper-class street, is now surrounded with "modern" industrial buildings, warehouses, and Miss Emily's house looks like a decayed structure whose prime has long since departed.
Modernism comes into the story with a vengeance when a deputation of the town government arrives at Miss Emily's house to tell her that she needs to pay her taxes. Unfortunately for the modern part of the town, the Old South raises its head (in the form of Miss Emily) and tells them Miss Emily has no taxes--that they had been remitted permanently by Colonel Sartoris years ago. This very modern attempt fails utterly to defeat the Old South.
Later, when Miss Emily buys rat poison, ostensibly to get rid of "rats," the pharmacist tells her that (modern) laws require him to know why she is asking for poison, she simply looks him in the eye, and she wins another war between modernism and the Old South.
During the only incident in which Miss Emily actually does something "modern"--allowing herself to be courted not only by a blue-collar worker but a Yankee--the townspeople adopt very Old South attitudes and actually try to bring in relatives to talk some sense into Miss Emily in order to get her to act like the aristocratic southern lady that she still is. This also fails completely, another defeat, but this time the conflict is flipped on its side, with Miss Emily fighting to be modern,and the town trying to keep the Old South alive.
The town, in essence, represents to forces of modernism in conflict with the Old South, and Miss Emily, most of whose actions are relentlessly Old South, defeats the forces of modernism until her death.