How you conclude your essay about Alice Sebold's novel The Lovely Bones really depends on how you start it and what you say about it in the intervening body paragraphs.
There are many different themes you could address in your essay. One approach would be to focus on an individual character, discussing how that character gradually comes to terms with Susie's murder and manages to rebuild his or her life afterwards. In that type of essay, you could move chronologically, beginning at the start of the novel and continuing through to the end.
Another possibility would be writing a thematic essay. For example, you could look at how the novel addresses sexuality. In that case, you would start out with a paragraph describing the types of sexual relationship in the novel. Next, you would address each of the relationships (Susie's rape, her parents' marriage, the romance between Ray and Ruth), and then conclude by showing what the body of your essay has revealed about the issues you raised in your introduction.
As stated above, the main function of your conclusion is to show how the supporting evidence in the main body of your essay illuminates whatever claims you made in your introduction.