Kitty isn't stupid, her job is to extract the religious book that everyone has and she would go for the easiest targets, not especially fancy and thus probably well guarded ones.

So someone's Goodly Book would go missing, and then maybe two or three additional texts from some other people as she checks if there's more important scripture.

...Also, if people on this island do any kind of recreational reading, some mundane books would probably also go missing, because Kitty can't read thus will probably grab the wrong thing a few times.