Depends on what book you mean.
Of the green rulebook there exists five copies, one for each Dandelion leader. They're seen lying on the table when Ephemer, Blaine, Ven and Skuld are discussing things.
Of the Book of Prophecies there is assumed to be only one copy left, but we don't know who has it yet.
According to the Master of Masters only one of the five kids should have the Book of Prophecies and it should be a secret to the other four.
The book Blaine was looking into for creating the spirits was lying there in broad daylight though and the other four all saw Blaine ripping a page from it.
Oh, ok, I have a lot of confusion in my head regarding this matter.
Please no, that'd strip away any humanity that Elrena had, and make her very one dimensional.
You can't really say this without knowing a possible motive for the murder.
I doubt she would have murdered her on a whim, so whatever reason she might've had for doing it could be born out of some emotional issue, which is humanizing in a way. It's really ugly to think about it, but killing another out of desire (maybe she really wanted to be chosen as one of the leaders) is very human-like.
And I don't think it would make her one dimensional as much as make her character consistent, just as it wouldn't make Lauriam one dimensional.
I certainly prefer it over a random heel turn Ventus out of nowhere, just for the sake of the shock.