How does the author use foreshadowing in The Other Side of Dark?

When Stacy's older sister Donna visits, Stacy is shocked to learn Donna is married and pregnant. Stacy objects because she was supposed to be Donna's maid of honor, but Donna did not have a large wedding. This foreshadows the discovery of the many changes that have occurred in the McAdams' lives while Stacy was in the coma.