In 1771 Augusta was made lady-in-waiting to Queen Sophia. She became one of the most known socialites of the Gustavian Age and a centre of attention at court. Together with the ladies-in-waiting Ulla von Höpken (her sister) and Lovisa Meijerfelt, she was known as one of "The Three Graces", as expressed by Johan Henric Kellgren in his poem "Gracernas döpelse" - the Graces were the Goddesses of Joy in Greek mythology.
Augusta was admired for her elegance and good taste. Her sister Ulla was at one point the object of Prince Frederick Adolf's affection, and Augusta herself was in the 1770s involved in a relationship with Prince Charles. Her relationship with Charles lasted between c. 1771 until c. 1777 - it was publicly known and accepted, but she was not an official mistress. Their relationship was much talked about when Charles was married to Hedvig Elisabeth Charlotte of Holstein-Gottorp in 1774, and contributed to the distance between Charles and his spouse. She was eventually replaced as a mistress by Charlotte Eckerman and Charlotte Slottsberg. After her relationship with Charles ended, she continued to be known for her "unprejudiced" attitude in her love life.
Prince Charles' wife, Hedvig, described Augusta in her famous diaries: "She is with no doubt charming, her features are pleasant, her appearance appealing, and dressed for ball, she is quite magnificent". As for her personality, Hedvig adds that Augusta did not have a bad effect on Charles, and that she was a kind person who, due to her tolerant attitude toward others, was also treated tolerantly herself: "As it happened the other day, Countess Löwenhielm was late at dinner and arived a quarter of an hour after it had started, and unfortunately, Baron von Essen arived at the same time. All of us aware of their relationship found it amusing, and some could not hide a smile." Ulla remarked of the incident: "To think if something of that sort would happen to another poor soul - they would never hear the end of it. But my sister is always excused, and it can only be seen as proof of her open nature and her frankness to expose her relationship to that meek Essen for the world". Hedvig then replied: "She may not be more careful than others, but of a kind and goodhearted nature, she is friendly toward all and does not interefere in other people's business, which makes her less exposed to slander than most".
In 1795, Augusta von Fersen left court: her mother, formally head of the court of the queen dowager although in reality bedridden, was fired from her position and her daughters left the court in protest, officially to take care of their mother's health, and she was formally fired in June 1795. In 1799, she presented Lolotte Forssberg at court. Her last years were spent in religion and charity.