Terry Pratchett kid's books if she can read pretty well (also great for Mom/Dad to read aloud at bedtime)-
The Amazing Maurice and His Educated Rodents
Wee Free Men
A Hat Full of Sky
I didn't care for The Amazing Maurice, but the Tiffany Aching trilogy is excellent! And perfect for a 9 year old with a solid reading level. The heroine is bright and strong and funny, but still makes errors and is very much still a child.
I also recommend 'Talking with Dragons' by Patricia Wrede. I don't think the rest of the series was as strong but the firts book is excellent.
If any girls like unicorns the Firebringer Trilogy has them. Not the greatest books, but hey, unicorns!
I adored the Trixie Belden series when i was younger, but find them tedious now. But the Oz books still get an occasional read. Make sure to stick with the ones written by Mr. Frank Baum. Any by other authors are dreadful.
Adding support to "Matilda" by Roald Dahl.
Throwing in the first of the Potter books. Should be readable for a 9 year old with a solid reading level.
Also throwing in the Warriors series for boys (its about cats, think Tailchaser's Song). My 9 year old boy is going through the series at full speed.