Eugenie's dress at the royal wedding?

Okay the hats are fun. I get that. And Beatrice was wearing a very tasteful suit that looked nice on her. But I didn't get what her sister Eugenie was wearing. I'll admit I only saw one picture that showed the skirt and the wind might have been blowing it or something. But that skirt looked weird. I couldn't figure out what it was suppose to be doing. It looked like the hem had come loose or the inside was sewn to the outside or something. Can anybody explain that skirt?