The signifance of Sheila's book
I think the D-Hunter book is very significant in understanding Sheila's actions with Pairo and Kurapika.
When we look at Sheila's personality and actions is there enough evidence to determine whether she is good or evil? I don't think we can say for sure one way or the other, but I believe there is more evidence that Sheila was a good person.
We actually don't know much about her personality as a child. We see that she is very clumsy and obsessed with the book Dino Hunter, and becoming a Hunter.
We also see that she does not go along with the formation of the troupe and presumably leaves alone to begin her journey to become a hunter.
Flash forward to the events of volume 0. I think we see more of her personality here. She is still just as clumsy, but is now an adult and traveling solo. She is saved by Pairo and Kurapika and gives them the book she was obsessed with.
Why does Sheila do this? On the surface it is just a kind gesture of gratitude. I think there is more going on here though.
For Pairo and Kurapika, it was a way to learn the language and of course they also loved the book. But imagine how excited Sheila must have been. This was her favorite book she was always rereading - and now she was sharing in that excitement and love of the story with others!
Like a parent reads their favorite book with their child, it's about sharing that story that inspired you and passing that inspiration on to your child.
I think that's why Sheila gave them the book. She was an adult now and ready to say goodbye to it. She wanted to pass on that story she loved to another child. I think it really could be as simple as that.
Another small detail, the elder found the hidden location Pairo and Kurapika were keeping the book. If he was normally looking around there, he could have found Sheila first. This might explain her abrupt departure - he forced her to write the note and leave or maybe he killed her and forged it.
All in all, since we don't have Sheila's perspective nothing is 100% certain. My opinion is only based on the evidence we have of her, which imo sways more good than evil.
So what do you think is the importance of the book? I'm especially curious the opinions of those who disagree with me, and believe that Sheila had some malicious intent.