Sometimes these type of books can attract demons and the like, they sense the book and your curiosity and try to tempt you into using such
things.
Well, I'd say it's more your mindset than the presence of the book... Sounds like YOU opened the doorway so to speak, and curious entities locked
on, and came through...(or possibly just one entity, like the nearest to the doorway) Most such "doorways" are temporary (it's your focus on the
subject that keeps it open) and maybe a little cold turkey break from thinking of such things, will seal it up again... Different entities have
different ideas of what to do while in this realm...so who knows why it chose your sis instead...
Try a few minor techniques, such as burning sage, etc. to seal up the doorway (especially if you can find it...and your sis' room is a great starting
point...) Feel around for coldspots...(could be on a wall, floor, even ceiling, or just somewhere in the space of the room) Remember, it's really
your mindset in getting rid of it, more than the tools used...