You've hit the nail on the head, as far as this problem goes - during Catherine the Great's rule, there was not consensus (neither amongst her European ruler contemporaries nor her subjects of all classes) with regard to her power or her means of acquiring it (or her day-to-day actions, for that matter. She was a controversial person). Historical reviews of her actions are still split, which you're seeing now in your sources. Most of the sources I've come across portray Catherine the Great as a great political strategist who achieved her ends with sometimes unsavory means. She is often referenced as bringing the Russian Empire back to a state of greatness that it had not held since the end of Peter the Great's reign, something her husband was altogether incapable of. But that doesn't equate to a consensus, so, here are some generally well-reviewed books to further your research:

Catherine the Great: Life and Legend, John T Alexander Catherine the Great: a Short History, Isabel De Madariaga A History of Russia, the Soviet Union, and Beyond, David MacKenzie, Michael Curran