The answer: A sheet cake, decorated with a LOT of pink frosting, some blueberries (as a nod to health or a color contrast I'm not sure), and a plastic princess for good measure.
This one was barely a craft, requiring minimal effort and I debated posting it. But in then I decided that I would as a reminder to myself if nobody else. In this age of competitive Pinteresting and overplanning, it's nice to just go with the flow sometimes, to have no idea how a project is going to turn out, to make a cake and have a celebration just because you can. It was a joy to watch the girls with their cake.
It was also pretty nice to eat it when they were done. Yum!