Grief in the Fourth Dimension — Jennifer Yu

Jennifer Yu's Grief in the Fourth Dimension is a moving and unique speculative YA novel about the afterlife and the unexpected connections that can be made in death.
 
In life, high school classmates Caroline Davison and Kenny Zhou existed in separate universes -- Caroline in one of softball practices and family dinners; Kenny in one of NASA photo books and late-night shifts at his parents' Chinese restaurant.

But after their deaths, they find themselves thrown together as roommates in a mysterious white room -- one that seems to exist outside of time and space, shows them their loved ones' lives on a large hi-def TV, and grants their wishes with a sardonic sense of humor.
 
As Caroline and Kenny watch life continue to unfold back on Earth, they realize they can influence events through radio signals, psychic mediums, and electromagnetic interference. In their efforts to console their families, they also start to understand the tragic depth of how their lives and deaths were connected and how to help their families -- and themselves -- heal from the losses.