I am a project-finisher by nature, so it's useful to me to hear from other people who may operate more like DD.
My library habits are very similar to your daughter's. I like to read a little bit of a lot of stuff. I figure life is too short to waste finishing a book I feel done with. I always have lots of different books going at once because different books meet different needs - focused attention, fluff, fiction, nonfiction, etc. As long as you have a set place to keep books so stuff gets returned I think it is fine.
And, yes, my craft closet would probably also make you uneasy. In this area of my life I'm more about process than product. I like trying new stuff, learning new skills, enjoying the process. It works for me. I haven't had a problem being more focused in other areas.
If it is bothering your daughter that she isn't finishing then that's another matter. If she's simply feeling done and moving on, I wouldn't worry about it.
