There are bits that do work however. The character of Roz is a rather chilling look into how people can turn when manipulated and how it can take one thing to make people snap. She is arguably the best thing about the book and is written very well. And as previously mentioned, the present day narration works the best.
The main problem with A Dark Dividing is that it's difficult to know who Rayne is writing for here, as the content and the type of horror is tailored towards children (thereby excluding the adult audience) but there is also some content that is most definitely not for children or possibly even teenagers (I'm thinking of the sexual content specifically here). As mentioned earlier, you also have significantly older protagonists than childrens' or teen books tend to. As a consequence, it feels like an adult book aimed at children and that doesn't quite sit right with me.
It's also difficult to recommend it because who do I recommend it to? It does not know its audience, and for that reason I'm afraid I cannot really recommend it. If you have a friend or relative fluctuating between different ages, then this is the book for them. Otherwise, leave this one on the shelf.