I'm sure I will eventually think of more, and of course I'm a big fan of Princess Nell from The Diamond Age.

At the moment, I am thinking of Arcadia Darell ⚠️ ↗ from Isaac Asimov's Second Foundation, although at 14 years old in the story she is something of an old woman, and I am also thinking of the many girl characters in Heinlein's books (maybe 11yo Patricia "Peewee" Reisfeld from "Have Spacesuit, Will Travel" ⚠️ ↗), and also 8yo Irene ⚠️ ↗ from George MacDonald's "The Princess and the Goblin". All fine girls.