After her graduation from U.P., del Mundo was offered a full scholarship to any school in the United States for further training in a medical field of her choice by President Manuel Quezon. She accepted the offer and chose to go to Harvard, arriving at Harvard Medical School in 1936. She was unwittingly enrolled in Harvard Medical School, an institution which did not yet then admit female students. As recounted in her official Ramon Magsaysay Award Foundation biography:
Some sources cite del Mundo as the first woman ever enrolled in Harvard Medical School, or the first woman to be enrolled at Pediatrics at the school, or even the first Asian admitted to the Harvard Medical School. On this point, del Mundo herself would acknowledge only that she was "the first [woman] coming from [as] far [as the Philippines]".However, Harvard Medical School began to accept female students only in 1945,nine years after del Mundo was enrolled in the school.