River wears this pink sweater/skirt outfit in Safe, where she famously dances with the townfolk and then gets kidnapped.
More after the break...
All screencaps from Safe.
I thought for sure I had more caps of this costume lurking on my hard drive, but they are missing. I'll add more when I get them.
My Photobucket Album for River.
Serenifly Costumes site for River.