Oh man, my first thought(s) were Red or Granny shooting the arrow but the Huntsman is so more likely, lol.
I don’t know about MM regaining her memory as she is reading to Henry. I think it is just one of those emotional moments where she is thinking about how she had no one in the past. She says “When I first gave you this book…” She is going way back before Emma even came to StoryBrooke, before any interaction with David (other than flowers on her rounds). Something will wake her, but I don’t think it will be the book.