Yes, Joan Aiken! What about the series that starts with The Wolves of Willoughby Chase? I can’t remember what the series itself is called, if it has a name, but it’s absolutely great.
And another vote for Narnia here.
Damn, I can’t wait for my daughter to be this age…
John Bellairs. I adore his Lewis Barnavelt books (and the others are okay, too), but I thought they might be a little too scary for the OP’s girl. They sure scared me…
I loved Edward Eager’s storiesof children encountering magic. Still do, in fact. Start with Half Magic. He loved E Nesbit’s work, which I missed as a child. Well, it’s not too late & her works areavailable online. And Eager also loved Frank Baum’s Oz books. I missed them, as well, as a child; a friend still treasures her illustrated editions. Look, somebody scanned them onto the internet!
When we were very young, Mom bought a cheap set of children’s classics. Pinocchio, Little Women,* Little Men*, etc. Some were too old for us, but we “grew into” them. If you can afford it, buy copies of interesting books & let her get into them at her own speed. (In the old days, there were very few paperbacks for kids; that has changed.)
(I hope the kid finds some good stuff here; my reading list has definitely expanded!)
If Tamora Pierce hasn’t been brought up yet, her Lioness quartet (Alanna: The First Adventure, In The Hand Of The Goddess, The Woman Who Rides Like A Man, and Lioness Rampant) and her Immortals quartet (Wild Magic, Wolf Speaker, Emperor Mage, and The Realms Of The Gods) are both really good. There’s a tiny, tiny bit of stuff about sex and menustration, but nothing too explicit.
I wanted to second Dangerosa’s suggestion of Erin Hunter’s Warriors series, about clans of cats living in the wild that form alliances, fight one another, fight off other enemies, etc. My 8yo is devouring these eagerly, as her sister did before her, and I know several of their classmates love them too.