I think your other advice is great, but I do have a word of warning. I used to be like your DD when I was a child (and as an adult, to a lesser extent). The reason I did not finish projects was because in school, things were easy. But if I did something on my own, I was not used to having to put in the effort and hard work it took to finish a project. And my work never seemed perfect enough for me. I had countless sewing projects, cross stitch pictures and stories gathering dust in my closet. This is an area that I have struggled with even as an adult.
Perhaps you can work with your DD on a smaller project to get her used to following through with something. There's a lot to be said about the satisfaction of looking back at the hard work you've done and seeing a completed product.
Like your DD, I always had my school work done. But I could have used the practice of having to actually work hard or work long on something to get it finished.
Exactly--this was me! (not to say for sure this is what is going on with the OP, but worth considering).