Disney Themed Birthday Party, costume ideas?

Hey, I am going to a birthday party (In June) Its considered quite a big deal, so i've gotta get my planning started. I have been killing myself to get a flat tummy - which I achieved, and I want to show it off at the disney theme party. Princess Jasmine was my first preference, but the birthday girl wants it, so i'm not going to argue with that. I am not too sure about going as Ariel because of the tail, and I don't know if there are any designs that don't look silly for a green tail. I am blonde, blue eyes, about 54kg (110lb) and medium height. I don't mind dying my hair to suit the costume, but can somebody please help with an idea??? Thanks!