The book Thinner, by Stephen King, yeah...don't buy it for your niece for her twelfth birthday.
Even if she is smart and a very advanced reader.
Because when you read the back of the book where it tells you what it's about you may think it is an appropriate gift. When you read that it is a story about a man who accidentally runs into an old gypsy woman with his car and kills her and then her father puts a curse on him which makes him lose a whole bunch of weight (which by the way does not sound like a curse to me) you might possibly think it is an okay thing to get for your horror story loving niece.
But they fail to mention the reason why the man runs into the old woman in the first place. They fail to mention what his wife was doing to him while he was driving and why he was distracted.
However they do talk about it a whole lot throughout the entire book. Graphically.
For Christmas I'm gonna take her to a therapist.