I think we’re gonna see the Eva/Leo wedding in this ep. That dress looks like a wedding dress to me, and those big towers of white flowers look like wedding decorations.
It is actually the same dress she wears in The Miller’s Daughter – when Cora shows the court she can spin straw into gold.
Saw a tumblr post earlier that had a BTS pic from Miller’s Daughter of Eva in that dress standing next to Xavier who was sitting on his throne. I couldn’t remember even seeing Eva in that scene, but checking screencaps, she WAS standing there, with Henry on the opposite side of the throne, (which does sorta make it seem like maybe Eva was the favoured choice for his bride until Cora spun gold and knocked Eva out of the running). Seems odd that they’re re-using the dress, and having Eva wear it to a totally separate event as well.