This is the first book in a new series, which is sort of a companion series to her Immortals series. (But more appropriate for younger readers. So if you have a teenager who's reading about Ever, this would be completely appropriate for her younger sister.)
As readers of the Immortal series know, it pretty much opens with a car crash. Ever, her parents and younger sister Riley and their dog, Buttercup, die in a car accident. For much of the first book, Riley "haunts" Ever but then crosses on.
In this book, we learn what happens to Riley after she stops visiting Ever.
At first, Riley's afterlife is pretty sweet. She lives with her parents and dog in a house and neighborhood that's identical to where they lived when they were alive. She can manifest whatever she wants and do whatever she likes.
Unfortunately, she soon has to get a job because the afterlife isn't just hanging around, doing nothing.
She's assigned the job of "Soul Catcher," which means she gets to return to Earth and help ghosts cross over. Her first assignment is a boy who's been haunting a castle for hundreds of years.
I really enjoyed this book–not sure what that says about me, since it's so clearly written for elementary and middle school kids. ;) But it's very fun and while there are scary ghosts, I don't think it would be too scary for little kids. (And there's also a little lesson in there about facing your fears, so that would probably help, too.)
I also think Riley is very relatable for kids. She's smart and sarcastic, but she's also scared and overwhelmed a not-small amount of time in the book. But, since she always overcomes it, she would probably also be a good role model.