The Catholic Church now has 35 Doctors of the Church. These are Saints whose writings and doctrine are of great benefit to the whole Church. They are known for the depth of their understanding and the orthodoxy of their theological teaching, and they have contributed significantly in at least one area of Catholic faith. For example, St. Basil the Great is known for his support of the Nicene Creed in opposition of Arianism, and is also considered by many to be instrumental in the growth of communal monasticism.
On October 7, 2012, Pope Benedict XVI gave to the Church her fourth woman Doctor. St. Hildegard of Bingen. joins the ranks of St. Catherine of Sienna, St. Teresa of Avila, and St. Therese of Lisieux. St. Hildegard, who lived in the twelfth century, was declared a saint by a process of ‘equivalent canonization’ in May of this year, which extended her liturgical cult to the whole of the Church and made it possible for her to be named a Doctor of the Church. She was a writer, composer, philosopher, mystic, Benedictine, visionary, and contributed a great deal to the science of herbal medicine. She received many visions from childhood on, and as she wrote them down, she explained them with biblical exegesis - of all her accomplishments, this especially made her a remarkable woman in her time.
Unfortunately, St. Hildegard has been adopted by feminists and new age devotees alike. If you are interested in learning more about this remarkable woman, choose your sources very carefully.
For more information about St. Hildegard, the Catholic Encyclopaedia at New Advent is a good place to begin.