Journey to Cheshire Bay (The expédition Cheshire Bay) by Shander, H. M. NEUF

Iris is ready to clean up her life and start over. For real this time. No more drinking, homelessness, or failed suicide attempts. Her only viable solution is to ditch her past and move across the country to the small town of Cheshire Bay. As she boards her only means of escape, shes gobsmacked to see her seatmate is the nerd she tormented back in high school.
Holden has put the past behind him, including those awful years in high school where he was picked on for being smarter and younger than his peers. Grown up and filled out, hes ready to live his meticulously planned future, forty-four hours from takeoff. However, he has to get there first. That, unfortunately, includes a six-hour flight beside the girl who made his high school life a nightmare.
When the plane makes an emergency landing and the clock starts ticking, book smart Holden needs street smart Iriss help to get him home. Maybe together they can put their differences aside and navigate the challenges ahead. Maybe, just maybe, the road trip will change their view on the other forever.