At most the women "preached" to other women at convents, though never during the Mass as the sermon, which always was reserved to the priest. Your interpretation is a myth, much like the myth of early, ordained "deaconesses." The women so designated weren't ordained. The title meant that they were the wives of ordained male deacons, much as an "episcopessa" wasn't herself a bishop but was the wife of an "episcopus." Poor Hildegard's name has been attached to things she never really said.
More information about text formats