Guardian
Violet experiences premonitions as a part of her relationship to an entity that she communicates with in her mind, and she calls him Guardian, giving the reader a big hint as to the nature of the creature and their relationship. She believes this to be her guardian angel or guardian spirit, so a part of her higher self. This connection to her spiritual life serves her well, and it also helps her to be open-minded. In other words, although to Violet, the Guardian may mean one thing, to the reader, it's a symbol of her open-mindedness, creativity, and imagination, and it tells us that she is the kind of person who looks for meaning anywhere she can find it.
The flower twins
Twins are a helpful symbol because they are a sign of comparison and contrast. Because visually, twins look very similar, the question is automatically raised about what distinguishes them. In this case, they are distinguished by Kate's rejection of a part of her self. We know this because she abandoned the name Daisy, the name that linked her (by flower names) most closely to her sister, Violet. This is part of why she doesn't understand Violet's sexuality, because Kate isn't the kind of person that likes to explore herself in those ways; she's concerned with living a normal, good life.
The omens and portents
Throughout the novel, the sisters reveal their magical powers in their hyper-awareness of portents and omens. For instance, the major action of the novel surrounds Violet's claims that an earthquake was coming in October. An important note here might be that their prophecies have worked before in the context of the novel; a few years earlier, their supernatural insights helped to solve a serious crime mystery. To the reader, these omens are symbols of the meaning that we overlook in daily life. The novel seems to be saying that if we could pay closer attention to the minutia, and by using our imaginative minds, we can solve problems that seem impossible to solve.
The tragic downfall
When the reader finally realizes what Violet's prophecy was alluding to, the reader sees a tragedy unfolding in Kate's life. Violet saw a literal earthquake in her vision, but the reader understands that the earthquake is a metaphor for Kate's indiscretion. Now the downfall is tragic, of course, but it's important to remember that when Kate and Hank sleep together, their spouses are away on a business trip. Although the reader knows that Kate and Hank are sort of an item, the implication is that at work, the same thing is happening, so it's not necessarily an excuse to demonize Kate for her behavior. Nevertheless, the omens were certainly intended as a sign that Kate's behavior would be like an earthquake, destroying the home she built for herself. She will likely end up divorced.
The motif of human connection
The novel is about human connection, broadly speaking. We learn about the explorative, open intimacy of Violet and her new girlfriend; we see the struggling sisterhood, one sister having rejected her name which associated her to the other one; we see friendships, couples, affairs, marriages—all with one common element in common: There is more to the relationship that it seems on the surface. For instance, Kate and Jeremy seem happy, and they have a beautiful family. Their family friends seem like lifelong friends in the making—their kids play together every day. But secretly the kids play together every day because while Jeremy and Courtney are at work (probably dating), Kate and Hank are raising their pretend family together (definitely having an affair). The question of human relationship is not answered, but it is on display throughout the book.
