How did a young girl, almost unknows to the great majority of the inhabitants of Lima, who lived as a semi recluse, become a saint just after her death, venerated by hundreds who came to play homage and approach her body to obtain relics and the cure of disease? To answer these questions, this paper analyzes the role played by Luisa de Melgarejo, the circumstances surrounding the death of the girl, and the infleunce of the Dominican Order in generating a climate of opinion which made possible the start of the beatification process. An important element in this last, is the life of Rosa written by a member of that order a few days after her death, and which can which can be considered her first hagiography.