As the first answer notes, the Faulkner believes that Emily deserves a rose, but in a 1959 interview, he explains exactly why he titled the story "A Rose for Emily."
First, Emily began life as a young woman with "aspirations to find love and then a husband and family." But as we know, Emily's father--a stern, harsh aristocrat--denied her a normal life, preferring to keep Emily under his control in part by finding that none of Emily's suitors is ever quite good enough for her. As Faulkner himself puts it,
[Emily was] brow-beaten and kept down by her father, a selfish man who did not want her to leave home because he wanted a housekeeper. (Faulkner, "On 'A Rose for Emily,'" fromFaulkner in the University, 1959)
Faulkner goes on to explain that Emily's horrible crime is the result of the "sad and tragic manifestation" of Emily's inner conflict between what she desires--a normal life of love, husband, and children--and the denial of that life by a father who should have had her interests, not his, in mind. In a sad and perverted way, Emily constructs her version of the perfect life--but, in the process, breaks the moral and civil laws she is brought up to honor.
In the end, Faulkner himself bestows upon Emily the rose, a symbol of the love she so horribly chases throughout a life blighted by her father's selfishness and cruelty. In Faulkner's words, the rose symbolizes the "simple things which all human beings want."
Since the story "A Rose for Emily" never mentions a rose, readers are often confused by the title. William Faulkner is said to have answered the question by declaring that the story itself is a tribute to Miss Emily, so the rose stands for an honor bestowed. The author's explanation need not be the final word in discussions of literary interpretations, however, so other theories for the rose in the title have been suggested.
One idea is that it represents romance. Roses are the most common flower we associate with romantic relationships nowadays; people often send roses to their beloved on Valentine's Day. Miss Emily's romance with Homer Barron is the defining moment of her life--a time when she appeared to be happy-go-lucky and in love, but a time from which she could not move on, as exhibited by her murder of Homer and subsequent preservation of his corpse in her bed. So although the story is ultimately about murder, it is also about romance.
Some have suggested that Homer's corpse is the rose--a dried, pressed rose as a memento of a happy time. When Emily's bedroom is opened for the first time in forty years, the narrator describes the rose-tinted color of the room. This could signify that the room itself is the rose, preserved for Emily's reflection for decades after she ended Homer's life.
Finally, the rose is a symbol of secrecy. The term sub rosa, or under the rose, means secretly. Roses were carved on ceilings and on confessionals to remind people of the confidentiality of the conversations that took place there. Faulkner's story is full of secrets: the Baptist minister won't divulge what happened in his meeting with Emily; Emily won't tell the druggist what she wants the poison for; Emily's servant Tobe never talks to anyone about what goes on at his mistress's house; and Emily keeps Homer's death and interment in her bedroom a secret for forty years. Thus the title could be another way of saying "Emily's Secret."
Faulkner's interesting and enigmatic title for his short story allows many interpretations.
There are a couple reasons why the title includes a rose in it. First of all, two main subjects are apparent in this story: death and love. The opening scene has Emily after she has passed away. The rose could be the parting flower used to bury a loved one. Roses represent death in this aspect. Death occurs 3 times in this story, too. Her father died, Homer died, and finally Emily died.
Second, the rose is known for romance and love. Emily never received love from anyone. Her father never let men near her, and Homer only wanted to move on with his life. He would never settle down. So the title could mean that she finally TOOK a rose for herself. She had to do what she had to do in order to keep "love" in her life. In doing so, she had to kill her lover. So death and love are intertwined in this aspect.