We really can't point at one hairstyle for emo girls and say This is true Emo Hairstyle, because one of the most important things in being Emo is to be individual as much as you can be. But then again there are some basic elements you should keep in mind. First and very important:
Be sure to grow your hair all out; by doing this you'll manage to cover large part of your face. After your hair is big enough you can, dye it black or blonde (the most popular emo girls colors).
Then straightening your hair is also not a bad idea, you can do this with the help of hair-straightener and then there is the final step; style your Emo Hair.
By doing that you'll achieve your unique individuality. There are many ways to style your Emo Hair, you just need some imagination, you can also use some hair accessories such as butterfly clips or hair bands! Good luck with your new Emo Hair!