After watching “The Return” and “The Stranger”, I’m thinking Mother Superior/Blue Fairy wrote the book.
The theme and message of the book is “Hope.” The blue fairy was desperate when she spoke to Gepetto about Snow’s child being the savior. The Blue Fairy was the only FTL character to have witnessed most of the stories in the book – an important point. She works in the school so she could have easily placed the book. The blue fairy mentioned she “had to make preparations with the other fairies” before the curse reached them in the castle. Could she have created the book from magic?