Girl in Translation

When kimberly enters the campus of harrison prep on her way to her interview, she hesitates for a moment and thinks about "turning back, going back to who i was." Why is "going back to who [she] was" not possible for kimberly at this point in the story? in what ways is "remaining who she is" not necssarily the same as "going back to who [she] was? That is, how do you believe she should try to preserve her personal identity without being afraid to change at the same time.