The 11-year-old girl George Lucas mentioned is the character Ahsoka Tano, a new Star Wars character to be introduced as part of the animated Clone Wars series premiering next Fall.

Thanks to reader Guiguioh for tipping me off on this!

I did some looking about this character and here is what I found:

Little has been publicly announced about this new Star Wars character except that she will be a Padawan learner of the Jedi Knight, Anakin Skywalker. She is said to be of the same species as Shaak Ti, Togruta. Ahsoka is described to have a personality between Obi-Wan Kenobi and Anakin Skywalker. She is to be voiced by Ashley Drane.

I have to admit I hope this is not going to be as much of a main character as Lucas made it sound. It just that an young pre-teen girl character seems a little too young audience focused for me. I guess we will see.