Headcanon: When the Pevensies first began their reign, huge gowns were in style for events such as balls and galas. It was Susan’s idea to introduce thinner and lighter dresses, similar to the ones they wore casually, in a much more elegant way for balls. This style didn’t just catch in Narnia, but also Galma and Archenland. The noble ladies were very impressed by the young girl’s boldness to introduce new fashion.
(Gif from costumehistory and tonsofgifs)