Last One Alive by Kristopher Rufty
It was only supposed to be a relaxing weekend away from the drab of regular life, but what it became was a fight for survival. Megan is pursued through dense mountain woodland by a psychopath she doesn't know, a relentless nightmare she can't kill. No matter how she tries to stop him, he just keeps coming back, even stronger than the last time, chasing her deeper into the wild, and closer to a trio of despicable hillbillies who are sadistic on another scale. Lost in woods populated by pure evil all around, what hope does Megan really have?