The handbag should be small and formal, and include a wrist strap for her to hold it securely while dancing. Encourage her to carry only the necessities, such as lipstick, wallet and cell phone. A wrap could be a light shawl, shrug or jacket. Remember that the evening is not likely to be cold, but the ballroom could be over-air conditioned. Choose a wrap that is lightweight and easy to carry. Jewelry should match the formal prom dress, but it is ultimately the choice of your prom girl.