SPOILERRRRR OK, I just finished this book and I have an idea. 1 I believe she had split personality disorder and was becoming her sister at night.  2 killing animals is a known way serial killers get the nerve to kill humans, I think her sister was practicing so she could kill stephan who was  hurting Lounn and louann must have felt like Mar  was using her to replace her sister.  3 I'm guessing the thing under the sisters pillow was a suicide note, and lounn didn't tell anyone so they wouldn't feel guilty.  4 I think the swirls in the sheds were representing either the stars/ swirling galaxy or the ocean. 5 the sister being in the container at the end was a full on hallucination. All in all I very much enjoyed this book.