I agree with the previous statements and say you should do the classic Snow White.
I think the classic princess gowns can be just as sexy, if not sexier, than the Halloweenish "sexy" costumes. It's all about the attitude you put behind it, and how you portray Snow White.
I agree with the sentiment that the others gave; you will look like you're trying too hard/seeking attention.
Those are just my opinions.