A very good book is "Drawing on the Right Side of the Brain". My mom gave me a copy when I was young and I really appreciated how it taught me new and novel ways to consider art and drawing. It left a very big impression on me and really assisted in my art skills.
You may also want to tell your daughter that some of the best artists of "childish" looking art are actually masterful illustrators (Picasso, Mondrian, Calder) so if she puts the effort into developing her art skills (which it sounds like she's interested in doing) she actually may be able to return to those innocent roots eventually and feel that spark of discovery again. Sounds counter intuitive, but has been demonstrated in art history, and I've experienced it myself. Almost like the more you know, the more freedom you will have to do what looks simple.
Sometimes the art my young children create looks so perfect in its simplicity. Your daughter may never draw exactly like that again, but if she gets the right instruction she will probably appreciate the world that will open up to her.
