Kit also has a tomboyish charm to her-baseball, robin hood, treehouses, writing stories...
Kit is the only American Girl with a "boy" friend-Stirling(I think when they grow up the 2 of them might even get Married!). Maybe Kit's Friendship Fun book would have some more unisex things, unlike Samantha and Ruthie who are total girly-girls.

Think of Ruthie, the girly girl, Stirling the boy, and Kit the in between tomboyish-girl. What kinds of things did they do together? Maybe that could give you some ideas...