Ideas for 9 year old girl?

I want to get my 9-year-old cousin 3 books for Christmas, since I'm getting her 14-year-old sister a trilogy and sibling rivalry means they need similar types and amounts of presents. (Besides, I love reading, and would really like to get both of them to love reading too.) But, while I have more ideas than I need for her older sister, I have no idea what to get the 9-year-old. She is currently in 4th grade, and reads at grade level.

She often starts books, loses interest, and doesn't finish them. I already tried giving her Matilda and some of the other Roald Dahl books (the BFG, and the 2 Willy Wonka books, since she liked the Charlie and the Chocolate Factory film), but she wasn't interested in them. (Maybe they were too low of a reading level? While Amazon says a lot of the Roald Dahl books are for ages 9-12, I read them when I was 4, and I've seen threads about parents introducing their kids to them at ages 5-6. I mean, I still love them - great children's lit is great at any age - but I don't know if appropriate reading level is an issue with her not finishing/being interested in things, or if she just didn't like them. I've tried asking why she doesn't like certain books and what she thinks might interest her, but she doesn't do a lot of reading for pleasure and I don't get a lot of helpful responses.) She does like the Harry Potter books she's read.

I'd like to get her the first book in the Animorphs series, since I know I liked those books when I was younger and they're individually not very long, but I don't know what to buy for the other two. Since I don't know if she'll lose interest in Animorphs before the end of the 1st book, I don't think I should buy books 1-3 in that series. Would the first book in the Percy Jackson series be a good idea? I remember reading The Giver in school in 4th grade and loving it, but Amazon calls it a YA book.

Can someone help me out with some suggestions? Something about the level of the first 2 books of the Harry Potter series is probably about right for her reading level, and she finished both of those. Suggestions with strong female characters would especially be appreciated - I'm trying to segue her older sister from obsessively re-reading Twilight into enjoying other supernatural/dystopian/paranormal YA series with female protagonists stronger than Bella Swan.

She seems to have a strange combination of higher-level books and sporadic reading. I have one of those myself! ;) The Giver is a good book for older kids; I think 4th grade is probably just fine for it if she's made it through Harry Potter. Percy Jackson is fine content-wise, but the history and mythology may go over her head a little and it focuses on the male characters a little more.

My suggestions for you to look into:

The May Bird trilogy is exceptional, but they deal with death and the afterlife (in a fun Tim-Burtony way).
Coraline
The Mysterious Benedict Society series
Theodosia series (strong young female detective... snarky but not bratty)
The Apothecary - I got this on ER, and really liked it. The lead character is an American girl who moves to England. Magic, mystery, a tiny bit of romance.
The Incorrigible Children of Ashton Place
The Secret Order of the Gumm Street Girls - a wild take on the Wizard of Oz. LOVE this for young girls.
The Phantom Tollbooth - my favorite book ever, which I read in 4th grade. Lots of wordplay and whimsy.
Princess Academy and The Goose Girl - very strong female characters
Terry Pratchett's Tiffany Aching series (though I hear book 4 may be darker than the rest, the first three are wonderful)
Blue Balliett's books

My 8yo likes anything to do with animals: Magic Puppy, Unicorn School, Freddy, Babymouse (comics), Molly Moon

and anything with mischievous girls: Ivy and Bean, Ramona and Beezus, Just Grace, Judy Moody

Obviously I could go on for days... HTH some. :)

eta: touchstones :/

Does she like Enid Blyton? eg. these three?

The Enchanted Wood by Enid Blyton
The Magic Faraway Tree by Enid Blyton
The Folk of the Faraway Tree by Enid Blyton

I started reading the Animorph series the summer after 4th grade, it was one of my favorite series growing up.

For a strong female character, maybe you could get her Dealing With Dragons, the first book of the Enchanted Forest Chronicles.

For the older cousin, has she tried any of Lois Duncan's books? Or The Hunger Games?

Peg Kehret's books may be a good choice, for those who don't read a huge lot. Especially the Frightmares series, for the 9 year old. The author's books would also appeal to teens, and the author is current. A lot of Peg Kehret's books involve animals.

One of hers I read recently that has a bit of fantasy and I liked, is Ghost Dog Secrets.

Thanks so much, everyone! I've definitely got more of a place to start (and, fortunately, a bit of time before Christmas shopping has to be done, so I'll have more time to try to decide.)

For my older cousin, I'm getting her The Hunger Games for Christmas and possibly the LJ Smith Night World or Secret Circle series for her birthday - like I said, the older cousin is easier to buy for, especially when (with the Hunger Games) a movie release is imminent. I know she hasn't tried anything Lois Duncan, though.

UnrulySun, thanks for the long list - I know she hasn't read any of the books on it! I love The Phantom Tollbooth myself - that might be a really good suggestion. And I'll definitely look into the others - I haven't read Coraline, but I like Neil Gaiman, and hopefully she will too (starts to plan...this year, Coraline, then Stardust a couple years from now...) The suggestions for books with animals might be a good idea, too; she likes animals, which was part of the reason I thought about Animorphs for her.

The Enchanted Forest Chronicles sound really familiar for some reason...I think I might've read and liked them when I was younger.

I think that I may end up buying her the book #1 for a bunch of different series, to see which she likes best - as I said, she hasn't had a ton of exposure to a wide variety of books, so part of this is going to be trying to find out if she knows what she likes.

Tamora Pierce has a series about a girl who becomes a knight (the first female in her country to have done so without being disguised as a man!).

Protector of the Small

MCFReadAloud, reading the description, that sounds like it would be perfect for her. I think that one's definitely getting ordered for Christmas.

The Freddy the Pig books by Walter R. Brooks are wonderful, as is anything by Daniel Pinkwater.

Maybe the Betsy-Tacy, the Shoes books by Noel Streatfield...

When I was nine I loved Karen Hesse, Uri Orlev, John Bellairs (particularly his Johnny Dixon series), the My Father's Dragon series, and Karen Cushman's books.

Also, comic books! The old Uncle Scrooge and Donald Ducks comics are so wonderful. I might never have become interested in novels except my dad's a librarian so I was literally stuck in libraries for hours at a time.

I think that Love Ruby Lavender is a great book. Boh my sister and I read it in 3rd grade.