We have started discussing our costume options!!!

I think my wife and I are going to Disneybound as Belle (wife) and "Prince Adam" (me).
Costumes for my siblings are a little bit trickier because the party is going to be a surprise that we aren't going to tell them about until we are there - maybe not even until the day of. I am thinking we will get them each shirts that I can pack in my bag and give them to wear that day.
I know my sister (15) will want to do Ariel. For my brothers (14 & 11) I am thinking superhero shirts would be easy enough and if we choose ones from the Marvel universe it should be "Disney" enough. I just have to figure out which superheroes they like.....
I told my mom she has to get a Snow White shirt and we will get my step-dad a Happy tshirt...

I'm not being nice. Anyway... My wife and I already have our clothes picked out, and the superhero shirts will be easy enough to find but does anyone have a good idea/suggestion for an Ariel shirt for my sister? I don't mean a shirt with Ariel on it but a shirt that might make her look similar to Ariel. She is my little sister so hopefully nothing too provocative.....