I envy people whose kids want to be this same thing for Halloween from one day to the next. My kid changes her mind daily. Right now my plan is to get an Elsa costume as I think that's the most consistent request, but also pick up a pair of fair wings she could wear with a dance costume, and keep her old Moana costume in reserve as a just in case. I think they our bases are covered unless she has one of those days where's she's like "I thought I was going to be a sloth? Can you get me a sloth costume by tomorrow?" In which case we're screwed.
I want to like Halloween, but I just... don't.