What happened to Dana and the 15th Armored Battalion? The start of Robotech: The Next Generation explains what happened when the Invid invaded. The Army of the Southern Cross was apparently wiped out, but was Dana Sterling and the 15th Armored Battalion also wiped out?
Dana appears in the comics Robotech: Love and War and Robotech: Prelude to the Shadow Chronicles so it would seem that she survived the destruction of the 15th Armored Battalion and may have continued the war against the Invid in some capacity, but after that her fate in unknown.