What defined katniss's costume for the opening ceremonies in the hunger games?

In the opening ceremonies, each district is required to wear something that represents their district. In district 12, they represent coal mines. So, in the past games there have been costumes in the opening ceremonies about coal such as naked bodies with coal sprinkled on them, and other horrible costumes that Katniss doesn't like. So she is worried that she will have a bad and enbarassing costume for the opening ceremony.