This next paragraph, whilst not having any spoilers, may not make sense unless you've read the book. For some reason, I felt as though Megan's confusion throughout the book was unnecessary. Thinking of it objectively, as events and emotions separate from the story, I can understand why she was so confused throughout parts of the book, but put together with the story itself, it just seemed over the top and was one of the biggest things that annoyed me about Megan. Although we saw Megan's character visit the school psychologist, it would have been nice to maybe have a professional opinion written in as to why Megan was mute, rather than just the occasional references to guilt and the aggressive voice in Megan's head that frequently made an appearance. I understood that witnessing her best friends death caused her to go mute, but it may have made her more relatable if we knew why it caused her to stop speaking rather than sink into depression, for example.
I would recommend reading this book, it did have potential to be amazing, and it ended up settling somewhere in the 'okay' realm. Unspeakable is probably something to read to kill time, rather than a book to clear your schedule for. I enjoyed it nonetheless.