Okay, we'll give you a smidge more context. In the last chapter (which takes place a year after Trivia Night seals the fate of Perry), Celeste is all set to speak out against domestic violence. Her whole life has changed by this point: she's sold her seaside mansion, she's working again part-time, she's busy raising her two traumatized little boys...and she's doing the seriously hard work of coming to terms with her abuse.
Part of that work is speaking (scary) in front of other people (scarier) about her history with domestic abuse (scariest). She's literally trembling. There's a dude next to her—she thinks he's a psychologist—who also looks a little nervous. She thinks back to Bonnie, who never had to do any time behind bars, but has to do approximately a bajillion hours of community service. Luckily, Bonnie is a do-gooder who already serves the community for fun.
Yeesh. The event is starting. That means Celeste is almost literally quaking in her boots. But she's committed to speaking out, especially once she hears that the guy next to her is also a victim of domestic abuse. Suddenly, she gets a wave of courage. This guy needs her to stand up and share everything, to come clean, to give voice to the scared and voiceless.
So she starts her speech with the words "This can happen to anyone," which are also…the last words of the novel.