Check out Kiki Strike. It's a favorite of mine for giving girls in her age range...

Also, did you know that the original Nancy Drew books were reworked in the 1950s (I believe) to make her less strong and to dumb down some of the language? You can tell the difference between the two versions because the older versions have 25 chapters vs. 20. I'm building a collection of these for my daughter and frequently find them at garage and library sales.