Symbolism, Imagery, Allegory
There are five Golden Retrievers in We Were Liars: Poppy, Bosh, and Grendel belong to Penny and Cadence, while Prince Philip and Fatima belong to Harris and Tipper. Penny is a breeder (of dogs, though she obviously bred a human as well). In describing their Beechwood house, Cadence says, "Windemere is gabled and angular […] The rooms are airy and filled with dogs" (9.2). Cadence refers to them as "the goldens," and they're a central part of her life. They're also the one way Penny brings in a little (very little) money.
When she describes her grandparents' dogs, Cadence says:
Fatima and Prince Philip ate starfish on the shore, then vomited them up in the living room. They shook water from their shaggy fur, snarfled people's picnic lunches, chewed Frisbees into hunks of unusable plastic. They loved tennis balls and would go down to the court and slime any that had been left around. (75.45)
The dogs are beautiful, but kind of useless. Unlike hunting or herding dogs, they don't have jobs—so while they're pretty, they're also purebreds that require a lot of upkeep and offer little output. Who else do we know who's blonde, rarefied, and high-maintenance? Ah yes, the Sinclair sisters.
Prince Philip and Fatima are sacrificed, along with three of the Liars, in the Clairmont fire. Cadence realizes the dogs are dead; then, in short order, she realizes Johnny, Mirren, and Gat are dead. Remembering the dogs' deaths is a necessary stepping-stone on the path to remembering the Liars'. Upon her recollection, Cadence says, "How could I have been so wrapped up in my own stupid criminal exercise, the thrill of it, my own anger at the aunties and Granddad…?" (75.50). Her desire to bring down the patriarchy took down innocent victims.
Cadence's fairytales all deal with three of something, and at the end of the book, there are three Liars gone and three goldens left. And there are still three sisters, who are still beautiful and high-maintenance, but irrevocably scarred by fire. Both they and Cadence learn the hard way that self-righteous anger carries with it the risk of casualties.