The anime has all the elements of the book--or, at least, most of them--but the order is a bit different and the story has clearly been modified slightly to conform with Japanese culture.
For example, in the first episode, the Murrays are going to have a lottery to see who has to take care of Emily--and although Emily draws Elizabeth Murray's name, Elizabeth negates the outcome of the lottery before Emily can really say anything, by saying that it's her responsibility, anyway, as head of the Murray household. In the book, Emily draws Elizabeth's name, and that's it.
Perry, the child laborer that works for Cousin Jimmy in the anime, isn't (as far as I've seen yet) in the book. He might be in the story later, though, as the anime series has switched the order of many of the incidents of the novel.
In the novel, Cousin Jimmy is thought to be "not right in the head" following a childhood accident. Even better, he refers to Emily as "pussy". The way Montgomery dwells on Jimmy's supposed mental insufficience, and the way he keeps having Jimmy call Emily "pussy", Jimmy comes across as a really, really creepy person.
(I know that the book was written in the early 20th century, back when "pussy" didn't mean "female genitals"--at least not in polite society--and that Jimmy's nickname for Emily was perfectly innocent at the time the book was written. But things have changed since then, and now it's kind of gross.)
Anyway, the story is not a bad one, although I am still wondering if Emily doesn't suffer from some kind of schizophrenia, what with all that stuff about Wind Woman and fairies and elves and stuff. Montgomery doesn't make it very clear that Emily has a vivid imagination, instead presenting her imaginings as if she was actually seeing them--like they were hallucinations or something.
But, what the hell. The book has long since been in the public domain and it cost me nothing but some paper to read it--I can't sit at the computer and read 200+ pages of text--so WTF. And it's not a bad story, either.