This is a great question! Of course, one of the the most striking descriptions of Miss Emily comes in Part I of the story, when she is described as a drowned corpse that had inhabited the sea for a long time and thus was bloated and swollen:
She looked bloated, like a body long submerged in motionless water, and of that pallid hue. Her eyes, lost in the fatty ridges of her face, looked like two small pieces of coal pressed into a lump of dough as they moved from one face to another while the visitors stated their errand.
This description highlights the depiction of Miss Emily as a character, who, in some senses, is already dead - she is isolated and trapped in a different time period whilst everything is changing around her, which symbolically ties in with the theme. It is interesting to note that she at first does not accept the fact that her father has died. Note the madness in the family that is referred to. Lastly, the grey strand of hair that lies on the pillow next to the corpse of her "lover" suggests that she is one who is in love with the dead, and that having killed him, she herself has "died" metaphorically to be with him forever, again symbolically relating to the theme. She has created her own happy ending, and thus remains an enigmatic, isolated figure until her own death, symbolically representing the theme of the enigmatic, isolated, lost and dead South.