if you mean what can you BOTH go as, like the same thing... me and one of my friends are going as Crayola Crayons. some friends of ours are going as Elmo and Cookie Monster. Bonnie and Clyde is awesome. Twins (wear the same stuff, die your hair the same, one person acts as a shadow.)
different colored crayons
moster high
vampire
BOYS: mummies GIRLS: witches
The popularest girls Halloween costume is the goth zombie prom queen.
a m&m
Cats/kittens there cute and a goddess YEP
Sailor moon and other Sailor senchis.
playboy bunnies
As long as it is not past Halloween, it isn't too late to get a costume. Costume stores are open on Halloween and days before.
Umpire is a Halloween costume. It begins with the letter u.
You can buy costumes for girls at many department stores, costume shops, and even on the internet. If you are looking for something unique and different stick to the costume shops and online sites. You could even try having a costume custom made, that's sure to wow your daughter's friends.