It is relatively easy to find out about any book by looking online for reviews or a synopsis prior to reading it. If it is considered fantasy, sci. fi. a novel, or of a sort that may be unsuitable reading for a Catholic, learn that in advance. If in doubt, don't read it. Books involving the occult, glorifying witchcraft or paganism, automatically reject. Once read, it cannot be unread. There are so many good books out there, why take a chance with evil? For that matter, many books aren’t evil, but are just drivel, not worth the paper they’re written on. They’re the junk food of the literary world. A steady diet leaves one weak and sickly. Look into good, time-proven literature if you enjoy fantasy or fiction. Be discerning just as you would before adopting a diet.
The saints have long warned against bad books and bad companions. If they were on earth today, they’d be warning against bad internet, bad social media, bad TV, bad movies, bad video games, and in the 1930’s-1950’s, against bad radio shows. All of these hold today including bad books. Just because something is lo-tech or old-fashioned, doesn’t mean it’s good. Don’t believe me? Prior to the League of Decency, there were some very racy movies, even before the talkies!
We have the internet today, so there’s no reason for Catholics to innocently stumble upon a bad book to the point that a demon enters a teen girl’s bedroom! A 16 year old should be learning this good use of internet to make wise decisions about library books.