Complex sentence: Millard's last major role was as Agnes Wickfield in "David Copperfield" at His Majesty's Theatre in December 1914; while her last known role was a brief appearance as Calpurnia in "Julius Caesar" during the Shakespeare Tercentenary Celebration in 1916.
Split into simpler sentences: Millard's last major role was as Agnes Wickfield in "David Copperfield" at His Majesty's Theatre in December 1914. Her last known role was a brief appearance as Calpurnia in "Julius Caesar" during the Shakespeare Tercentenary Celebration in 1916.