Thank you all for your suggestions!
DD eventually settled for Red Riding Hood. I bought an inexpensive piece of red fabric and a length of red satin ribbon from the fabric/ notions store and quickly made the cape, it took me 40 - 45 minutes max! She's wearing it with a white tube dress from T-shirt material that she calls her Pool Party Dress - I had made it for her to wear as a swimsuit cover up!
I can re-purpose the cape, by putting the fabric to use for some of my craft projects for upcoming Christmas craft fairs and/ or make fabric gift bags!
Alternatively, I might just keep the cape for my younger daughter's use! My next door neighbor hosts a costume party/ contest at his riding school just before Christmas. Last year, youngest DD went as Tinkerbell (I made a green tube dress for her, and added the wings I made for her about 5 years ago when she was an angel in the school's Christmas)
We had quite a bit of fun coming up with costume ideas out of what we had or could easily make. My personal favourite was the Mob Boss (Black slacks, black blazer, black shirt, red tie, black fedora with a red feather, my nephew's toy gun, and a wad of Monopoly money sticking out of the breast pocket) Unfortunately it was voted out in the interest of comfort - Barbados is too hot for an all-black, multi-layered outfit!)
I'm not into Halloween at all, but I love coming up with costume ideas. It's the perfect marriage of craft and thrift, my two favorite activities!