Just to develop the suggestion made in #4, a great essay question would be to compare and contrast the different reaction of Susie's family to her death and how they respond to the aftermath. You also might like to think about how the family moves through or reflects different stages of grief on their way back to wholeness. Another question might be does the memory of lost ones ever leave us.
Another possible essay question could examine the students' interpretation on how Susie's death affected the members of her family and her friends. How students' interpret another's mourning is always interesting. It also sheds light on the students' character as well.
One good essay question for practically any work of literature would ask students to explain in their own words why and how they find a particular part of the work to be especially well-written. How or why is it memorable? How or why is it effective as a piece of writing, not as an expression of a "theme" or idea. How are the author's choices of words effective? How would a sentence be changed in effectiveness if synonyms were substituted for the words the author actually chose?
Because symbolism plays such an important role in The Lovely Bones, a novel written by Alice Sebold, it is a relatively easy to create an essay question about that literary element. One question I often ask students who read the novel in my class is, "What do the "lovely bones" represent? How are they symbolic?" I also ask students to "Explain how Susie's charm bracelet is a symbol. What does it represent and why?"
If you prefer a question that is more open to interpretation, you might ask, "How might Susie have reacted differently to Mr. Harvey if the story had taken place today? Why?" Prior to reading the novel, we discuss general societal differences between today and the early seventies, especially as it relates to violence.