With a lot of fabric paint, cutting, and sewing, I was able to transform an old flannel shirt into a Marie Antoinette inspired top.ETA
Here's the long version of how I made this top: I cut the collar and the sleeves off. I made the armholes and sleeves smaller for a better fit and added a little puff at the top of the sleeves. I also cut the bottom of the shirt in the front shorter and created a tail in the back.
I was originally going to bleach and dye the shirt, but after two attempts at bleaching I discovered it had NO effect. So I had to scrap that plan and turn to fabric paints instead. I used Tulip brand, colors Ice Blue Pearl, Carnation Pink Pearl, and Azure Blue Metallic. I applied the paints in a random pattern with makeup sponges. This took me about two days (one for the front, one for the back). I also used a stencil on the front, so the original pattern could peek through.
After waiting for it to finish drying, I hemmed the edges, added lace to the top and sheer fabric, ruffled, to the sleeves.