How does the author use foreshadowing by introducing Antonia into Olivia and Penelope's lives?

Olivia's recollections of her time in Ibiza not only play a part in explaining and describing Olivia now, they will play a key role in the future plot lines of the novel as well. Her relationship with Antonia and the fact that Antonia gets along so well with her mother, Penelope, will become evident later in the novel.