When my baby sister was a kid, I started getting her the Alice books by Phyllis Reynolds Naylor. The books went on and on so I kept getting them for her and, when she was old enough, I started getting them for the Lone Star Girl, too. I am about to start getting them for the Lone Star Baby and the Lone Star Niece, although I know I will have to hunt for them and order them now because the last book in the series has finally come out, Now I'll Tell You Everything, and bookstores are not really carrying the earlier books much anymore.
I love the Alice books because they are about an open-minded girl who learns and grows. Alice is not a prude and she decides her own mind - she is not just a convenient moral fable for kids. She is not a fantastic student, she is far from perfect. She is caring, though, and she is curious and she has a great deal of integrity. I highly recommend the Alice books for any growing-up girls in your life. Not counting the prequels, they start when Alice is in 6th grade with The Agony of Alice and continue until she is an older woman.