Complex sentence: She clearly mastered some basic aspects of it, and understood significantly more than she used in her own speech, but her rate of acquisition was very slow and resulted in her vocabulary being much more advanced and sophisticated than most people in equivalent phases of grammar acquisition.
Split into simpler sentences: She clearly mastered some basic aspects of it, and understood significantly more than she used in her own speech, but her rate of acquisition was very slow. This disparity resulted in her vocabulary being much more advanced and sophisticated than most people in equivalent phases of grammar acquisition.