Aix Marks the Spot by Sarah Anderson

Jamie has been dreaming of this summer forever: of road trips and intensive art camps, of meeting cute boys with her best friend Jazz. What she didn’t count on was the car accident.
Exiled away from her family as her mother slowly learns to walk again, Jamie is sent to Provence and trapped in an isolated home with the French grandmother she has never met, the guilt of having almost killed her parents, and no Wi-Fi. Enough to drive a girl mad. That is, until, she finds an old letter from her father, the starting point in a treasure hunt that spans across cities and time itself. Somehow, she knows that the treasure is the key to putting her shattered family back together and that whatever lies at the end has the power to fix everything.
Armed only with a high-school-level of French and a map of local train lines, she must enlist the aid of Valentin, her handsome neighbor who’s willing to translate. To save her family, she has castle ruins to find and sea cliffs to climb; falling for her translator wasn’t part of her plan…