I'm a student of the 5th Alabama Battalion, a sister unit of the 13th Alabama Infantry Regiment, when both were a part of Archer's Brigade of the Army of Northern Virginia. The 13th Alabama was NOT at the battle of Nashville.
Might I suggest that you try this posting on the Civil War Flags Message Board at http://history-sites.com/cgi-bin/bbs53x/cwflags/webbbs_config.pl , perhaps some of the flag experts there can help you figure out, from which unit the flag was captured.
Jim Martin