There are many opportunities writing an essay based on "A Rose for Emily." If the essay writer were a reporter, he would look for some aspect of Emily's life that was unusual. Here are some ideas that might work as a topic:
Senior Citizen Refuses to Pay Taxes
Miss Grierson Announces Upcoming Nuptials
Barron Missing for Six Months
Citizens Concerned about Foul Odor on Street
Black Servant's Disappearance Circumspect
Cousins Find Gruesome Scene in Grierson Home
Any of these headlines could be used as both a scandalous essay topic. As far as a thesis statement, remember that you are making an argument. So for the first headline, you might use the claim that "Even the most respected senior citizens must pay taxes."
Writing from the standpoint of a reporter does make the essay interesting. I believe that you will have fun with this assignment.