Her magical power is beyond the scale their tool can measure: 9999 is just the max their crystal can display. What it means on a practical standpoint is that she has ridiculous amounts of raw power, and can also immediately understand magical concepts and spells just by seeing them once. All of her spells will be ridiculously more powerful than any normal person's, and if she sees a spell once she can immediately cast it herself, only much more powerful than the original. Basically, when it comes to magic, anything you can do she can do better.