I read this book last year. It was probably YA, and I think the protagonist was called Liz, although it doesn't sound quite right. I remember most of the plot, just not the title.
Liz wakes up on a ship in a cabin with another girl (I think her name started with C), who explains that they're dead. The girl explains that Liz and she are both dead, and she shows Liz the bullet hole in her head. Liz assumes she's dreaming. When they arrive at their destination, Liz's dead aunt greets her. She takes Liz to her house and explains how Liz is going to age backwards now, and how they say their age in the place (physical age followed by how many years they've been dead, I think).
Liz's aunt takes her to the observation decks, where she can see her family. She watches her (traffic safety themed) funeral (she died by being hit by a car while on her bike). She keeps watching, becoming addicted to watching her family. Then she wants to talk to them, so she goes to a forbidden well place to try to talk with them. A police person a few years older than her (physically) catches her and gets her out. I think his name is Owen.
Liz and Owen inevitably meet again, and they inevitably are in a relationship, because apparently a young adult novel is not a young adult novel without a heterosexual relationship involving the protagonist (sorry, I'm editorializing; the relationship was actually okay in this one). Owen, however, has been dead for many years, and he left behind a wife. His wife dies, and predictable confusion ensues, and she's allergic to Owen's dog. Eventually she says that she's changed and Owen's changed and they're not compatible anymore, so Owen and Liz remain a couple.
It ends with Liz reaching an infant state and being sent down a river to be born again as three-year-old Owen watches (well, he's kind of distracted, but he's there).
That's a lot of information, I guess. I do a thing where I forget a title but remember everything else that happened in the book. Anyway, does anyone know what book this is?