Sally is thirty-eight-years old when she is killed; then, she begins to narrate Black Dog Summer.
A novel can be narrated by death (like Markus Zuzak's The Book Thief), a dog (as in Edward Wroblewski's The Story of Edgar Sawtelle), or a drug (consider James Hannaham's Delicious Foods).
So, the decision to have a ghost narrate a story isn't fresh.
"Ghosts make great narrators. They tend to see everything," explains Javier Marías, whose mystically-populated collection of stories While the Women Are Sleeping was published in Spain in 1990. (The interview is here, marking the English publication of the work in 2010.)
This is true of Black Dog Summer; Sally sees everything about her sister Adele's life with husband Liam, daughter Bryony and son Tyler, and Sally's surviving daughter, Gigi, who comes to live with them.
What could be better than an all-knowing ghost narrator who can observe and intuit what the average narrator might miss, who can seamlessly inhabit the experience of other characters?
More detail about this novel is here, on BuriedInPrint.