I don't know that there is a way to condone a premeditated murder of a man, but I think there is textual evidence to suggest her motives and from there, the reader can decide what level of sympathy Miss Emily deserves.
Early in the story the narrator reveals that Miss Emily's father held the family name and reputation in pretty high esteem, and therefore, he felt that any of the suitors Miss Emily might of have were not good enough for a Grierson, so he drove them all away (if they ever existed in the first place). After her father's death, Miss Emily is utterly alone in the world and out of touch with the people of Jefferson. When Homer is courting her, she can imagine a real life for herself, but once the rumors about Homer start, and she suspects that they will never marry and that he may leave she has to stop him. She can't allow Homer to get away, so she takes the matter into her own hands and kills him so that she can keep him under her control. She arranges his dead body in an upstairs bedroom and goes on to sleep with his corpse for at least a few years after his death (as evidenced by the length and color of the hair found on the pillow next to the corpse). The ending of the story is absolutely gruesome and her actions are perverse, but the total portrayal of Miss Emily by the narrator actually draws the picture of a sad, pathetic woman who the audience, like the townspeople, begin to understand better as the whole story of her life is revealed.