I have one of those dresses I picked up from the thrift store, laid it out on a twin flat sheet I picked up somewhere and hacked around it and sewed for an hour (mainly b/c of my dumb machine's bobbin kept tangling)
And then, I couldn't resist making a "matching" dress out of the pillowcase for my kiddo. Basically on that one, I cut off the top, cut down about a quarter way for arm holes, hemmed the arm holes, made a casing on the two tops and strung ribbon through the casings and tied at the shoulder. The material is rather thick, think it will look better on her tiny body with a thinner pillowcase.
So, we both look like we are wearing a trash sack as my hubby so gently put it, but we match and we'll be in the garden with them anyway. I call it good for about an hour and a half. Boy do I hate sewing.