The first female hymn writer about whom we know anything of substance is Hildegard of Bingen (1098-1179), called "Sybil of the Rhine." An author, theologian, mystic, specialist in natural history and medicine, she was consulted by bishops, popes, and kings. She founded a convent where she composed and presented music and plays. Her music has become oft-recorded in recent years and is widely available on CD and increasingly in hymnals and songbooks.
She is sometimes referred to as St. Hildegard, although she has been beatified but not yet canonized. Hildegard's music is commonly included today in college music study. Hildegard's hymn, "O Holy Spirit, Root of Life" (The Faith We Sing, no. 2121), makes use of more than a dozen images to describe the Holy Spirit's nature and activity.
For more information on Hildegard of Bingen, see "The Life and Works of Hildegard von Bingen (1098-1179)"