I am not a medical doctor. I did have correction that was around -10 when I was 8 years of age, and now have -17 diopters at age 37. I would recommend that your daughter be under the care of a pediatric opthalmologist and look into using gas permeable contact lenses for correction as she will have the clearest vision, if she can tolerate them. She should always remain under the care of an opthalmologist because she will be at statistically higher risk of certain eye problems (e.g., retinal detachment, myopic macular degeneration) There is not a lot known about why certain eyes elongate more in certain individuals (I cannot find very much on pubmed.gov). Most of the research generated seems to be coming out of Asian countries where myopia is considered a big problem. There is no current scientifically proven method to curtail the growth of the eye, however, treatments like atropine and the use of bifocals have been tried.
There is continued debate whether excessive near-work combined with genetic factor can facilitate the elongation of the eye in certain, susceptible individuals. Cross-cultural epidemiological studies seem to be the most supportive of this theory (although I believe that most mainstream U.S. opthalmologists downplay the influence of excessive near-work). My personal experience combined with my own research has led me to believe that it can only help to balance near-work with activities that rely on distance vision, as well as to develop good near-work habits (google Singapore and myopia to find more info.). Best wishes.
You don't have much say about how tall you child will be and the same goes with the amount of myopia she has. In the past bifocals, eye drops, rigid contact lens and avoiding near tasks have all been tried without much success.
She should see a Eye MD physician ophthalmologist to make sure there are no myopic degenerations of the back of the eye.
Find one in the USA at www.aao.org
JCH III MD