One of my most valuable writing exercises was to convert my "best" fanfic into an original work for submission to a serious "young authors" sci-fi anthology. It turned out to be very instructive as to the merit of my work, or more correctly to the lack thereof. (As opposed to the quality, with which merit should not be confused.) My story was not selected for publication, which did not come as a surprise.
I agree. Some writer or other once said "The way to learn to write is to WRITE!". The way for DFG's daughter to find her voice and her style is by doing lots of writing, and seeing what works.