Catherine the Great changed Russia primarily by modernizing and westernizing it. She implemented various reforms in governance, education, and culture, which helped to elevate Russia's position in Europe. Additionally, she expanded Russia's territory significantly, acquiring new lands through military conquests and diplomatic efforts. While she did reform aspects of the economy, her major contributions were generally seen in the broader context of modernization and territorial expansion.
Thus, the best response is: She modernized and westernized it.