Better coaching is likely key as it is in preventing injuries generally. As I recall, the girl that got injured was a shorter player playing in a front line position, but too far back. It is possible that she was put into a front line position she was uncomfortable playing, so she backed off and made errors.
Then there is the question of talent pool. Larger schools have larger pools to draw more outstanding and rare athletic talent from. It used to be that geographic districts and grouping schools competitively on size worked pretty well, but with school choice and private schools recruiting atheletes, size is not as good as it used to be. The lineman at our tiny school were small and they'd have gotten killed if we played a team from the big city schools, which is why we didn't. I don't have the solution to the talent disparities in modern HS athleticsl