In 1768, she became overhofmesterinde (Mistress of the Robes) to queen Caroline Mathilde, after her predecessor Anne Sofie von Berckentin had been unable to serve because of Caroline Matilda's disapproval that her original mistress of the robes Louise von Plessen had been replaced without her consent.
She belonged to the influential figures of the regency regime of Juliane Marie alongside kammarfrue Sophie Hedevig Jacobi (married to the king's reader Chr.
Jacobi), Juliane Marie's secretary Johan Theodor Holm and crown prince Frederick's governor Professor Sporon; she is described as ambitious and reportedly used her influence for petitioners whose cause resulted in disagreement between the royal court and the council.
Riegels participated in the 1784 coup that deposed Juliana Maria from power, and he dedicated a publication to Margrethe von der Lühe.
The same year, Margrethe von der Lühe remarried Christian Frederik Numsen (1741-1811) and left court.