Until It Hurts To Stop, by Jennifer R. Hubbard

Back in seventh and eighth grades, Maggie was the victim of a series of bullying incidents.  Years later, in high school, she is still terrified of being attacked.  In the intervening years, she has learned to use outdoor activities (hiking, in particular) to escape her anxieties and build confidence.  But this year, her former nemesis returns to the school, and Maggie's fears come back full-force.  Worse, her friend and hiking partner Nick is becoming interested in other girls - something which Maggie never expected to bother her.

The romantic subplot won't win any originality points, but the story stands out for its depiction of the PTSD-like qualities of recovering from adolescent bullying.  Hubbard does an excellent job of showing how the years of abuse cause Maggie to live in a state of constant anxiety, in which she in fact chooses to stay (ironically, for the comforting security it brings her!).  Two particularly remarkable scenes occur near the end where Maggie confronts her former enemies to find to her shock and surprise that they have moved on and forgotten everything (and that Maggie is no longer the center of their interest).  Other subplots (including the romance) are carefully tied in to the main theme and illustrate other aspects of bullying and of recovery.