I’m at level 37 and nicki simpson want “rainbow any sparkle” but Idk what I have to let her wear?

I just used the long multi colored sparkly dress from the collection called "extra"

The rainbow is satisfied by anything that has a multi-color dot next to it. The sparkle is satisfied by items with little star shapes below the style indicator. Additionally, the game will put satisfactory items at the top of each category. Hope that helps!