Books for preteen girl

My daughter is an avid reader. She enjoys mysteries, ghost stories, animal stories, and adventures. Books/series/authors she has already read:

Nancy Drew
The Black Stallion (she is on this series currently)
Phantom Stallion
Conspiracy 365
Hardy Boys
Mary Downing Hahn
Neil Gaiman
Fear Street
Goosebumps
Animal Ark
Suddenly Supernatural
39 Clues
My Sister the Vampire
Edgar & Ellen
The Books of Elsewhere
Shiloh
Where the Red Fern Grows
Because of Winn-Dixie
Homecoming by Cynthia Voigt (she wasn't interested enough to read the rest of the series, which I loved!!)
Jane-Emily by Patricia Clapp
The Ghost Next Door by Wylly Folk St. John

Those are just the ones I can think of off the top of my head. I tried to get her interested in the Warriors series but she hasn't read any of them. She is really wanting to move up to the teen section and has gotten some books from there, but I am leery of the content in a lot of them. She has asked the librarians at our local library for help in identifying some authors she might be interested in, but 95% of their suggestions are books she has already read! If anyone has any ideas about books she might enjoy, I would appreciate the feedback.

Well, I notice the Boxcar Children series missing from your list. I don't recall what actually happens in them, but I enjoyed (and still do, lol) the same sort of books you've got listed and I adored the Boxcar Children books. Also really really loved Madeleine L'Engle's Time quintet (beginning with A Wrinkle in Time). Roald Dahl? His are mystery/adventure types and fabulous for all ages. LJ Smith has suddenly become quite popular due to the TV series, but I read her Secret Circle series when I was around that age, when they were new!, it's about a group of teen girls who are witches.

My daughter is reading the Neil Flambé mysteries, and she loves them. There are only four books in the series so far—she got three of them for Christmas and bought the fourth with her own money yesterday. They are about 300 pages each, so fairly complex.

Are the classics of interest? Heidi, Little Women, Anne of Green Gables. All have good sequels. Personally, I always return to Eight Cousins by Louisa May Alcott when I want to feel like a cozy child again. I re-read Little Women when I need to be reminded of how to be a good mother.
I also read and loved Tom Sawyer, A Connecticut Yankee in King Arthur's Court, Kidnapped, and so on.

Oh! I forgot to mention Peter Pan, probably because I read it as an adult. It is an exceptionally good book to read aloud together. The language used, and the clever ways expressed, are far superior to experience from the text rather than say, the Disney version. My daughter and I used it as a way to stay connected through her adolescence.

Remember, you asked.
You hit one of my favorite buttons. I used to be a childrens librarian and then worked in one of the mega-bookstores. I LOVE recommending to your daughter's age. There is so much!
Has she read any Tamora Pierce or Diane Duane? Duane's Young Wizard series is excellent. Better than Harry Potter, in my opinion. Anything by Tamora Pierce - I'd start her with Protector of the Small series or Winding Circle series. They are not only entertainment. They help to instill deep values. You'd probably like them too.

The Trixie Belden mysteries should be right up her alley. Elizabeth Enright's The Saturdays and sequels is good. Phyllis Whitney wrote some good youth mysteries The Mystery of the Haunted Pool was my favorite. The Three Investigators is another series I really loved as a kid.

Thank you all! I have ordered a few of the books suggested through inter-library loan. Keep the suggestions coming!

I just finished listening to the audio of So You Want to be a Wizard, the first in the Young Wizard series; and I am again so impressed by it. The writing is powerful; the themes are deep and worthy of reflection.

Reminds me to recommend another fantasy - The Princess Bride. It's written by the screenwriter of the movie version, and is, possibly, better than the film.

There is a series of mysteries by Blue Balliet that she might enjoy. The first one is Chasing Vermeer. An older mystery/adventure series by Jane Langton starts with The Diamond in the Window. Eva Ibbotson wrote some very amusing ghost stories, and John Bellairs wrote some quite spooky ones. Even though they're old, they are still good. Bruce Coville is another author to try if she likes the supernatural. For animals and adventure, you might look at the Redwall series by Brian Jacques. My sons really liked Cornelia Funke's books at that age.

If she's interested in history (WWII) she might enjoy Once, Then and Now all by Morris Gleitzman. One of my favourite books aimed at her age-group is Tuck Everlasting but then I'm now in my 50s and might no longer have a good grasp of what appeals to a pre-teen. I do think some books remain classics for a reason though, and Tuck is one of those (as is Peter Pan (#5). You could also try some of Philip Pullman's books such as The Ruby in the Smoke, The Firework Maker's daughter and I Was a Rat; not only could she enjoy these now but they might lead to her later moving on to the His Dark Materials trilogy, another deserving modern classic