Who challenged Maria Theresa's right to rule Austria?

Maria Theresa's right to rule Austria was challenged by Frederick II of Prussia, who sought to undermine her authority and legitimacy. He invaded Silesia in 1740, sparking the War of the Austrian Succession, which was fueled by disputes over the Pragmatic Sanction that recognized her as the rightful heir. Other European powers, including France and Spain, also questioned her rule, seeking to exploit the situation for their own gain.