This question contains spoilers…
(view spoiler)[Spoiler alert: Am I missing something or was this a plot hole -- Amy says that she cuts deep gashes in her arms, but then it says that she's swimming and wearing sundresses, etc. at the cabins place where she's hiding out. How does this work? (hide spoiler)]
Annie Good catch from a quick-witted reader. The kinds of wounds she describes would take a very long time to heal (and might even have required stitches to close properly), and even after healing would remain livid (meaning bright red scar tissue) before fading to white (and this can take more than a year, depending on skin tone). They would never, ever disappear. I have very bad scars from glass cuts on my arm from 21 years ago, when a window I was leaning on shattered. The author should have looked into this more thoroughly; her error is corrected in the film.
Leslie her arm healed (she says something about it like "my arm feels much better, thank you very much). -- reread that part. (sorry, i don't know what page -- will try to find myself then re-post/re-answer.