Katharina was the second child of the liaison between Augustus II and Fatima; her older brother, Frederick Augustus, was born four years before.
Shortly after the birth of Frederick Augustus, the King married Maria Anna to his chamberman Johann Georg (von) Spiegel, but she remained as his mistress. Katharina was born during this marriage and legally used the name Maria Anna Katharina von Spiegel during her first years of life.
In 1715, her stepfather Johann Georg of Spiegel died. Augustus II took the guardianship of his children, but only recognized and legitimized both in 1724 and they were granted the title of Count and Countess Rutowska.
The now Countess Rutowska was married off by her father on 1 October 1724[3] to the Polishnobleman Count Michał Bieliński. The marriage was an immediate failure and after eight unhappy years, in early 1732, they divorced.
Contrary to what is written in several works, she did not die in 1746. From 1746 to 1752, she was in Turin with her husband the Count of Bellegarde, who was ambassador of Saxony.[citation needed]