Kaylee's prairie harpy dress was based on a 70s dress pattern. She wears it in Out of Gas and The Message.
More after the break...
The above is from The Message.
More screencaps from The Message here:
Screencaps from Out of Gas, with the back open showing her undergarments:
A signed photo signed by the cast featuring this dress (showing the boots she wears):
Another behind the scenes shot from The Message:
Dianne found the fabric for this dress here, pictured below.
My Photobucket Album for Kaylee.
Serenifly Costumes site for Kaylee.