We think that the grammar is pretty varied. Often it's easy to understand the sentences but sometimes the author is rambling on for pages and it gets hard to follow.
Most of the book is descriptions. It's very common that someone says just one sentence and that the following minutes is about explaining and describing why this person said what he or she said. It gets you a lot of free understanding but you can also get the feeling that you just want to move on in the story. Some of us have caught themselves missing and waiting for the dialogues to come!
The Lovely Bones isn't written in an old fashion language and the characters never speak in another dialect. Despite reading isn't so simple. We feel like many words are new to us because most of them never are used in the daily life. An example is the following quote.
"Then my wildlife photographers eye saw the tripods and silver circles rimmed by wire, witch, when a young man moved them left or right bounced like of or on the baby on her blanket"
If you look on the bright side the difficult wordlist homework gets very easy to do. Read two pages and you already got ten words!
If you think about it the language seems to be a little bit too difficult and mature for a 14-year old. But at the same time her appearance in heaven may have gotten her wiser. After all she knows everything she wants to know.