When I first wrote the Girl Power books I made Sims 3 versions of the characters. For no real reason other than to waste time I made Sims 4 versions of the 4 main characters. I think the one that was most improved is the Mermaid, who is basically Aquaman changed into a girl.
Her government-issued costume is basically a purple wetsuit with black leggings. I like the hair on this that has a slightly windblown look--or like she's underwater. She's just wearing flip-flops because no one has made flippers yet that I'm aware of.
I think the best part is it actually looks slippier like a wetsuit. The Sims 3 version didn't quite have that sheen to it.