Soon after the birth of her son, Mary had several conflicts with her mother-in-law. She planned to name her son Charles in honor of her executed father, but Amalia insisted that the boy be named William, which was a better choice: the first ruler of the United Provinces of the Netherlands was William I of Orange and in addition, the boy's late father also wanted to name his son William. Having won the battle for the name of her grandson, Amalia now wanted to become her legal guardian, referring to the fact that Mary was too young. On 13 August 1651, the "Hoge Raad van Holland en Zeeland" (Supreme Court) ruled that guardianship would be shared between Mary, her mother-in-law and Frederick William, Elector of Brandenburg (whose wife, Louise Henriette was William II's eldest sister); the Elector was chosen because he could act as a neutral party mediating between the two women, but also because as a possible heir he was interested in protecting the Orange family fortune, which Amalia feared Mary would squander.