Final answer:
St. Teresa of Avila established an order of nuns during the Catholic Reformation by founding the Discalced Carmelites, known for a return to the spiritual foundation of monastic life.
Step-by-step explanation:
During the Catholic Reformation, various new orders and reforms were established. One key figure who established an order of nuns was St. Teresa of Avila. She was a prominent Spanish mystic and Carmelite nun who founded the Discalced Carmelites, an order that focused on the return to the spiritual foundation of monastic life and was known for its poverty, simplicity, and contemplative prayer. Other notable figures include St. Catherine of Siena and St. Clare of Assisi, who both made significant religious contributions during their lifetimes, but the establishment of an order of nuns during the Catholic Reformation is credited to St. Teresa of Avila. St. Angela Merici founded the Ursuline order, which undertook the education of young women. However, in the context of the Catholic Reformation and the establishment of new religious orders during that period, St. Teresa of Avila is the correct answer to the question.