Who knows? There are a lot of factors to consider, is she the type of person who goes back over an event or part of story over and over in her mind until she completely understands it? Introverts tend to do that, if that is the case you don't want a kid to go over why Sasuke became evil, and trying to comprehend how Itachi felt when he did killing of his clan, let alone trying to get a deep understanding of pain's words and how he became who he was until her mind is satisfied with the conclusion, see- kids shouldn't do that.
If that's not the case, just let her read when she is in tenth grade or something, things will just go down in her memory as nothing significant and she would clearly not understand all the dark parts- her mind just skims over, kids remember stuff tough- which they later understand when they grow up, it's like how everyone thinks their parents is the world as kid and then later realize the difference between trustworthy/hypocrite whenever they mature(some people even die as 60 yr old kid)