I read it here that there was a book on japanese binding in her office, If this is not correct I apologize.
I think you probably read a post by a person more interested in demonizing Rebecca than learning about how she and Max died. If I recall correctly, the book was in a spare room at Spreckels that Rebecca had some paperwork in. It wasn't her office, per se, and there's no evidence, to my knowledge, that the book was hers or she'd ever laid a finger on it. I don't believe it was taken into evidence, either, but if I'm wrong on that I'm sure someone will correct me.
The person interested in demonizing Rebecca went on at great length in multiple posts about RZ's supposed affinity for "rope play." Again, to my knowledge, there is no evidence whatsoever to back up that allegation.