I was going to borrow a pretty dress and then make the cape, crown and sash. This is as far as we got.
I started with the crown and used this tutorial where you just coat some lace in mod podge a bunch of times until it's stiff enough and then sew the ends together. In the tutorial she paints hers gold but I skipped that. I did add a bunch of pretty glitter though. Next time I would use a thinner lace, mine may have been a bit much.
Then I made the cape. I really liked this one because it had a collar so it was my inspiration.
I basically took a rectangle of satin and added a couple pleats in the back, sewed on a collar and attached a hook and eye. I hemmed the raw edges and added some jumbo ric rac and it was done. Easy and pretty, if only she would keep them on. We didn't even get to the sash and pretty dress stage.
She sure looks cute though and I figure in a couple months she'll be ready for dress up and she'll use them then.