Wilhelmine's brother Frederick granted her an allowance in exchange for troops, following the same procedure with her sisters. With the outbreak of the Seven Years' War, Wilhelmine's interests shifted from dilettantism to diplomacy. Austrian diplomats were trying to influence the court of Bayreuth to take their side against Prussia. In September 1745, during the Silesian war, Wilhelmine met with Maria Theresa of Austria. This almost destroyed her intimate relationship with her brother. In 1750 Wilhelmine visited the Prussian court for several weeks and met famous contemporaries such as Voltaire, Maupertuis and La Mettrie. In June 1754, the siblings met for the last time, after which Frederick swore her his eternal loyalty. She acted as eyes and ears for her brother in southern Germany until her death at Bayreuth on 14 October 1758, the day of Frederick's defeat by the Austrian forces of Leopold Josef Graf Daun at the Battle of Hochkirch. Although Frederick had lost many friends and family to death throughout his life, Wilhelmine's hit him the hardest. He suffered from severe illness for a week following news of Wilhelmine's death and fell into a depression from which he never fully recovered.