What is Melanie's symbol?

Look to the chapter titled "Hieroglyphics" for this answer. It is chapter 14. At the beginning of the chapter, Toby suggests that they have a hieroglyphic system. His notion is that it will give them a written code to communicate about the Egypt Game while at school. Each kid will also have his/her own symbol that identifies them. Other than April, the other kids think the idea is quite interesting. April thinks the idea is "crummy," but that is because she can't think of a cool Egyptian name and symbol. Suddenly she remembers the "sort of cat goddess," Bastet. The statue of Bastet shows her as a cat with "mysterious eyes" and earnings. April figures that if she chooses the name Bastet, her symbol could be a cat's head with earnings. She tells the group her idea, and everybody loves it. In fact, her idea inspires Toby's symbol for himself.

If you were to pick the name of Bastet, your symbol could be a cat’shead with earrings. “Hey,” she said, dropping down to join the group, “I’ve got a great one.”
Everybody liked April’s name and hieroglyph. In fact, Toby said it gave him an idea for a hieroglyph for himself.

In the chapter titled "Hieroglyphics," Toby suggests that each of the Egypt game players choose an Egyptian name and corresponding symbol to identify themselves. By choosing special names and symbols, game players can remain anonymous in secret messages.
April is initially wary of Toby's suggestion but soon warms to it. She decides to call herself Bastet, after an Egyptian cat goddess. Her symbol, of course, is a cat's head with earrings. Toby chooses to call himself Ramose, after a famous Egyptian sage. His symbol is an owl. 
Meanwhile, Ken chooses to call himself Horemheb, Elizabeth goes with Nefertiti, and Marshall chooses Marshamosis. Last, but not least, Melanie chooses to call herself Aida, after a beautiful Egyptian princess who was held captive against her will. Melanie's symbol is a bird. She chooses the bird hieroglyph to identify herself because it stands for the letter 'A' in the Egyptian alphabet.