Professor McMillen specializes in Southern and women's history, with an emphasis on the nineteenth century. Among her publications are Motherhood in the Old South: Pregnancy, Childbirth, and Infant Rearing (Louisiana State University Press, 1990),  Southern Women: Black and White in the Old South (Harlan Davidson, 1992), and To Raise Up the South: Sunday Schools in Black and White Churches, 1865-1915 .  Professor McMillen is the liaison for the Southern Studies Concentration .  Currently she is working on a book about the Seneca Falls Convention of 1848 and women's struggle for equality.

Professor McMillen is the winner of the 2000 Hunter-Hamilton Love of Teaching Award.