In 1303, upon her mother's death, Blanche inherited the "señorío" of Alcocer. On 27 September 1305, she purchased for 170,000 maravedíes from Juana Gómez de Manzanedo, the widow of infante Louis, son of Ferdinand III of Castile, her inheritance in the city of Briviesca. She is considered the founder of the city as its sponsor and coordinator, and was also responsible for the founding of Colegiata de Santa María. "Her work was not limited to the urban planning of the new city, the layout of its streets (...) she also granted it a legal instrument for its governance and administration, the Fuero of 1313, which was inspired by the text of the Royal Fuero".