She-Ra is a female cartoon superhero and the sister of He-Man. She is a part of the Masters of the Universe series of cartoons and toys which were popularised in the 1980s. She-Ra is still embraced by those who grew up during that time. She is dressed simply, and thus makes a great do-it-yourself Halloween costume.
Start with a white outfit. Either a short white dress or a skirt and a bustier will work. She-Ra's outfit is short and sleeveless, so represent the look as best you can with what you can put together.
Modify the outfit by adding some gold and rhinestones to the top. She-Ra's outfit looks like it has a large, gold flower in the centre of the shirt/bustier with rhinestones in the middle of the flower. Create the flower by cutting it out of gold foam and using stick-on rhinestones to decorate the centre. Use fabric glue to stick the sparkly flower onto the top of the costume.
Make a headpiece. Create a headband shape out of the gold foam, and draw two wings on pieces of gold foam and cut them out. Glue or staple one wing to each side of the headband, so that each wing frames your face. Glue one red rhinestone in the centre of the headband. The headband should sit across your forehead.
Make the collar and armbands. Cut a thin strip of gold foam that is large enough to fit comfortably around your neck. Use adhesive Velcro pieces to hold it around your neck so that it looks like a choker. The armbands are simple pieces of gold foam that are long and go all the way from the wrist to the elbow, covering the length of the forearm. Staple or glue them together so they are wide enough to slip around your wrists and comfortably fit on your arms.
Put on a plain red cape, some gold boots (or boots painted gold) and finish the costume with a toy sword. Add a blonde wig or, if you are already blonde, wear your hair loose and flowing.