Elizabeth's Midnight - Aaron Michael Ritchey

Sixteen-year-old Elizabeth Meyers is an overweight, unhappy teenager enduring a dreary suburban life when her grandmother awakes from a catatonic state and announces that the two of them must go to France and solve four magical puzzles to reach a long-lost prince from another world. Elizabeth doesn't believe this, of course. She has no intention of helping her grandmother escape the nursing home, elude the authorities, find a way to steal passports and fly to Paris. And yet Elizabeth finds herself doing exactly that.