According to Spanish archives, she “suffered all the discomforts and dangers of the conquest.” De Guevara's correspondences paint one of the most elaborate, enduring portraits of the hazards of colonial life.
In one of her earliest letters, de Guevara described leaving 160 colonists behind as a defensive force while "400 men and some horses” went ahead to the new fort of Corpus Christi.
[1] She left Buenos Aires, when the fort there was deserted, to make the perilous 1,300-kilometre (800 mi) trip up the Parana River to Asuncion, the capital of Paraguay.
[1] In a letter she wrote in 1556 to Princess Juana of Spain, who was the head of the Council on the Indies, Isabel de Guevara argued that her labors entitled her to a partition of land and indigenous slaves.
She wrote that because hunger had caused the male colonists to “fade into weakness,” “all of the work was left to the women,” including civilian and military functions.