*One fairly minor spoiler ahead*
There's a very good story in here. I wouldn't doubt that the book is very good. However the screenplay, perhaps as well as the direction here really doesn't do the full story justice. Too much of the story is told from such an overly cynical and somewhat ignorant perspective of the older daughter by narration. Essentially this aspect alone robs the film of its overall effectiveness of being an entirely convincing film. Instead, much of the story the film tries to deliver through the narration, does not reasonably meet the actual story presented. So overall I have to say that while the film is decent, and does have a good story within it, this telling of it overall is not entirely effective enough. It's impossible to fully buy into, unless you care not to think about it much at all I suppose. I also have an issue with the part where child services takes the younger daughter away. If the oldest is 18, which she was, there should never be such a reason to do this. Unless there was some known reason why she could not care for the younger sister, which no reason of this is ever shown or even talked about at all in the film.
It really is too bad, because mostly I really enjoyed the story, and what the director and cast did here. Too bad the narration is not better written here to fit in better with the full story. It could've worked really well, and this would've been a really good little film, mainly if there were only less cynicism and narrowness of perspective in the narration.
5/10.