Alma Jr. said this to his son, Coriantor:
And this is not all, my son. Thou didst do that which was grievous unto me; for thou didst forsake the ministry, and did go over into the land of Siron, among the borders of the Lamanites, after the harlot Isabel. Alma 39:3
Isabel is one of only three (non-biblical) women mentioned by name in the Book of Mormon.