I was thinking sheer pink for the lips/nails too.

Let her choose!

Sheer pink ,peach or lavender. The almost neutral tones of those shades. The bright color of the dress is enough. Everything else should be subtle and complimentary.

Any of the bright young fun colors would be fine on her toes, they don't have to match her makeup. She could do green, blue, red hot, however she would like to express herself there....

I agree with Morz8 about the fun colors toenails. For the fingernails, buffed and shiny, but no polish, would look nice with the outfit, or a pale, natural pink. I get the sparkles, but with them, adding more can so easily go to overdone. Lips would be nice with a sheer pink or frosted gloss. If you look at the styling for the current crop of canary and rhinestone dresses (it's a popular trend), you'll see a lot of fresh faces (no make-up look), simple nails, minimal jewelry, if any, The point is that the color and sparkles are "unnatural" and make a nice setting and contrast for the natural beauty of the wearer.

I hope she has a marvelous time!