River is shown in Serenity as a student earlier in her life. (Interesting fact, the actress is Hunter Ansley Wryn, but voice you hear is actually Summer Glau. The ADR is fantastic in the movie.)
More after the break...
Some more screencaps:
The costume was up at the Propstore for a bit:
(Another random thought that has nothing to do with anything...I swear the brocade was later used here.)
My Photobucket Album for River.
Serenifly Costumes site for River.