Beyond the Billboard — Susan Gates

Almost nobody knows that thirteen-year-old Firebird Tucker and her family exist. Firebird is not allowed to leave their wilderness swamp hidden from prying eyes by a massive billboard, not even to go to school. And she must never, ever talk to strangers.
But suddenly, strangers are everywhere. And despite her family's insistence that nothing can change, everything does. In the midst of the turmoil, Firebird finally finds what she's been looking for--a way out.