It seems like bookends to me. In volume 1, she is in a terrifyingly controlling school which is hyper-religious. In volume 3, she is with a terrifyingly controlling hyper-religious wannabe missionary.

I'm not a literature major, nor have I ever read this book in a class with a professor who knew something. I just read it for fun several times. So this may or may not make any sense, but to me the goal was to show us something about self-acceptance and how it relates to our ability to forgive and accept the foibles of others.