The Undying: Shades by Ethan Reid

Synopsis (From Goodreads): The Undying: SHADES finds American student Jeanie and her young charge, Ren, fifteen years after the EMP that wiped out Paris and sent them on the run from the undying. Walking the highways and hiding out in abandoned buildings across France, they eventually find their way to Spain and the walled city of Ronda where a few dozen survivors have gathered—safe enough from the hunting undying, but facing a new threat on the scorched planet: starvation.