My pictures were too big to post in a comment, so I hope the extra post will be forgiven
This picture is taken with the side of the dress right in front of you, the pen on the right is showing the center back.
One showing the draw string tight, the way I needed it to look the most like River
And the same area stretched out
Also, the back has these button flaps that also gather the hem up a bit.
And one of those unbuttoned. They are on either side of the center back.
And then there is the front, where there is the bulge of fabric, like a shoulder, that hangs just above your knee. This is ther weirdest thing about the dress, and very hard to photograph, but here are some attempts.
Hope these can help a little. Some day I do want to try and make this dress, and I thing even with an original to look at, it will be tricky. Best of luck!