Maid Marian is a female character from the Robin Hood fable. She is the love interest of Robin Hood and is a princess who lives in Sherwood Forest. Typically, Marian is portrayed wearing a corseted, flowing medieval dress and a decorative headdress. It is an appropriate costume for a 12 year old to wear and making a Maid Marian costume is a relatively simple process. It is a good costume for Halloween or a princess-themed party.
Look through thrift stores for a medieval style dress with a corseted top. The collar of these dresses is often low and square and the sleeves and long and bell shaped. The skirt section of the dress will be long and flowing but the bodice will be tight and corseted. You can also attempt to make one of these dresses from scratch; patterns are available in books or on the Internet. A deep burgundy or dark green colour is good for this dress.
Wrap a gold sash around the waist and tie it into a bow at the back of the dress.
Choose a pair of shoes. Boots and slippers were common in this time period, but any comfortable shoes will work fine if the dress is long enough to cover the shoes.
Make a headdress. Attach lengths of coloured lace or different coloured ribbons to a headband so that the ribbons and lace fall down the back.
Wear hair long and loose. Choose long dangling earrings and add a few silver bracelets to complete the outfit.