My husband and I are HUGE Star Wars fans, so all our kids are stuck being Star Wars characters for their first Halloween. Our first born was Darth Vader. For the twins, I decided to reuse the Vader costume for my son and to make a Princess Leia costume for my baby girl.
I made a very simple white dress out of some white spandex material. I literally took one of her dresses, traced around it, cut the two layers and stitched it together. For the belt, I used a metallic, silver, net ribbon that I just tied on. The hat was a little trickier. I used brown felt and made a bonnet style hat. For the buns I just twisted strips of the same brown felt until it looked like a cinnamon roll then I tacked it on the bonnet by hand.
I wish I would have added some elastic to the hat so it would stay on her head better.