Emo is a term coined relatively recently to refer to a type of music in which the singers express deep emotion, often angst and pain. The followers of bands like this are dubbed "emo" as well, and can be identified by their penchant for wearing skinny jeans, chains and the colour black. Girls often sport shorter haircuts, while emo boys often wear shaggier do's and trucker-style caps. If you have an emo birthday girl in your life, she may not want the traditional girlie cake, so bake or order one made to suit her style.
The music scene is important to the emo community in general, so you can't go wrong by incorporating an emo chick's favourite band or instrument into a cake design. Find out what her favourite band is and have the decorator replicate their logo on the cake, or replicate the design of her favourite band T-shirt.
Some elements of the emo scene are a little creepy or gory, such as skulls or spiders, but these elements can be used artfully in an emo cake. Ask the decorator to create a standard girl's birthday cake and then ice a spider web draped over one side like a net. Alternatively, ask the decorator to create tiny skulls with bows on their heads where the icing roses would normally be on the standard cake.
Emo girls are still girls at heart, so don't cut out all the feminine elements when you are designing her cake. Some emo chicks will dig a cake that is covered with roses that appear to be wilting or hearts made with the icing dripping off of them so they appear broken. A way to keep emo cakes from becoming too dark and depressing is to use the more common girlie embellishments like iced butterflies or flowers on the cake, but use black icing to give them an emo edge.
If you don't want to decorate with the emo symbols of broken hearts and skulls, you can still create a cake your emo girl will love using a stylised colour scheme. Look at the clothes she and her friends wear to notice some patterns in their styles. Often the main colour worn is black, but accents of hot pink or bright plaids bring a little pizazz. Use these intense colours and patterns in combination with black when icing the cake, and you will create an emo cake without needing any advanced decorating skills.
Including feminine characters on a cake can be a more lighthearted way to make an emo cake. Have the decorator ice Tinkerbell in a black dress with her arms crossed, or give Hello Kitty a mop of black hair covering one eye. The contrast between the soft character and the hard attitude will make a striking cake.