Betsy~Tacy- Maud Hart Lovelace- it's a growing series, with each book getting progressively longer and more complicated. It takes place in turn-of-the-century Minnesota, with the final books taking her through European travel and marriage at the eve of WWI.
Caddie Woodlawn- Carol Ryrie Brink. Great for anyone who loves the Little House books. Caddie's much more tomboyish than Laura, though both are really great fun.
The Adventures of Tom Sawyer- Mark Twain. Classic, and my absolute favorite book at 8, so she may enjoy it.
101 Dalmatians- Dodie Smith. The movies are based on this book, but they are nowhere near as charming.
The Wizard of Oz series- L. Frank Baum. My favorite of these was
The Road to Oz, all about Ozma's birthday party.
Matilda- Roald Dahl. Great for any child who loves reading. Actually, any books by Roald Dahl are good except the adult ones (My Uncle Oswald, Kiss Kiss, and Switch *word for woman that rhymes with switch*). I particularly suggest
Charlie and the Chocolate Factory,
Fantastic Mr. Fox, and
Danny, Champion of the World.
The All-of-a-Kind Family- Sydney Taylor. Details the lives of a Jewish family on the East Side of New York in the early 1900's with humor and warmth. Has a full series, if you can find it.
Alice in Wonderland and Her Adventures Through the Looking-Glass- Lewis Carroll. Even if she can't understand the political satire now, she'll probably enjoy the whimsy.
Catherine Called Birdy- Karen Cushman. Fiesty mideval lady and a lot of fun all around.
Young Joan- Barbara Dana. The story of the life of young Joan of Arc. I loved this around that age, but it depends on whether you want to buy her religious books.
Some other books I loved-
Peter Pan,
Anne of Green Gables,
The Secret Garden,
A Little Princess,
Little Women,
Star Wars books (though those are a bit specific...),
The Adventures of Sherlock Holmes, books on Greek mythology- my favorite being
D'Aulaire's Book of Greek Myths,
Tanglewood Tales,
Number the Stars,
The Indian in the Cupboard, the
Little House series, and books by Jules Verne and H.G. Wells.
And those are just the ones I have on my shelves

I also have
A Series of Unfortunate Events and
Harry Potter, but these are ones I read somewhere around the same age. Of course, ever since I was 2, I've been reading everything I could get my hands on. I absolutely loved
The Hiding Place and
Pilgrim's Progress, but those might be a little heavy for her. My favorite book at 10 was
Catch-22, and my favorite at 11 was
The Hitchhiker's Guide to the Galaxy, but again, I was a really weird kid.