Our first shots of Ramandu's Daughter—or Lilliandil, as she's being called in the film.
She's surrounded by so much light it's hard to see some of the details of the dress. She's wearing a white, sleeveless (but with a slight flare off the shoulder like tiny cap sleeves), empire-waisted dress, with a V-neck and inset. If you look closely in this shot, you can see some tiny glitter spots—beads, perhaps?
From the display picture, it looks like there's an underdress that shows up at the V-neck (the inset), and possibly at the sleeve. If you look at her right arm in the display image, you can see what looks like a small sleeve under the cap sleeve. However, her arms appear to be bare below the cap sleeves in the trailer.
The skirt of the dress is full and drapey, probably a full circle. She wears a delicate bracelet on her right wrist.