First, you should define "setting," which refers to the time and place of a narrative. The Lovely Bones focuses on Susie's murder, which occurs on December 6, 1973, and its aftermath.

Next, consider that nature's seasonal changes are often used to represent/emphasize the stages of life. If you live in an area with distinctive seasonal changes, this is easier to notice in everyday life because spring, summer, autumn, and winter are marked by obvious variations in temperature, the amount of sunlight (vs. precipitation like rain or snow), and the activities in which people engage (working outdoors with gardens vs. staying inside because the gardens are dead of winter frost).

So, if Susie's murder occurs on December 6th, then it happens during a time of extreme cold, when the trees are bare, and the days are short. The narrative also states specifically that it is snowing and is already dark when Susie encounters Mr. Harvey.

Since the time and place of Susie's murder is distinctly not set during a period of rebirth, hope, or renewal, this is one way in which the time frame supports the novel's themes of grief and mourning.

(You can also extend the seasons metaphor to examine how the narrative discusses the characters' actions and Susie's observations in relation to the time of year.)