Catharta by Lauren Weston

Sarah Jenkins is just trying to get home from work late one night when she is unwittingly ripped from her predictable and mundane life and is transported to a strange and seemingly deserted land called Catharta. She quickly learns that Catharta is a gathering place of ghosts. It is a land built of memories and spirits. It is where the souls of the dead go to reflect on the life they lived and await rebirth. There, she finds that someone has been trapping souls on the other side, preventing them from gaining a second chance at life. The result is that these souls are imprisoned in limbo, and many people in the living world are being born with no soul at all. Sara has to find a way to free these lost spirits from their purgatory and save the world of the living from a soulless existence. But first, she has to find her way back into her own life, if she can.