do you have a pampered chef batter bowl? they make perfect barbie cakes or ask someone you know if they have one! they can go in the oven! and the small prep bowls make good little cakes if you want to make your daughter her own little cake and put a little barbie in it!
Yup, like babymaddy said, bake your cake in a bowl, turn it upside down, pry the legs off a Barbie and stick her torso in the cake (naked), and pipe on icing to make her dress top then pipe the skirt on the cake.