Embers in the Sea — Jennifer M. Eaton

After inadvertently saving the world, 18-year-old Jessica Martinez is ready to put adventure behind her and settle back into the familiar routine of high school. But when she's offered an opportunity to photograph the inside of an alien spaceship, Jess jumps at the chance. After all, she would be crazy to turn something like that down, right? Spending time with David on the ship has definite advantages and the two seem to pick up right where they left off. But when Jess discovers a plot to sabotage David's efforts to establish a new home for his people on another planet, neither David's advanced tech nor Jess's smarts will be able to save them.