Tiffany Aching from Terry Pratchett's Discworld series. She's more than just smart - she's sensible - and she's brave and loyal besides. She does the right thing not because she's a do-gooder, but because the right thing needs to get done and no one else is stepping up to do it. And she rocks because she's not a hero in a vacuum. She lives with the same insecurities and influences all girls do, and she makes the choice to look past the china shepherdess with its fancy dress to make a hero of her plain-speaking, tobacco-smoking granny instead.