She, alongside Ariel are the princesses of the Invid race.
Third Robotech War
After Princess Ariel (the first transmuted Invid) failed to report to the Regess, she created two more "childs" in the form of humans to find her. As the Crown Princess of the Invid Race, she and her brother Corg, shared command of Invid Legions, and they were both given Invid Commander Mechas.
With Corg, she fought Lieutenant Scott Bernard’s Robotech Resistance, being now in a humanoid form, she was also exposed to human emotions. Like her sister Ariel, she fell in love with one of the human resistance fighters named Lancer (aka Lance Belmont). Together, they convinced the Invid Regis that further war would bring the destruction of both races, ultimately siding with the humans. Thus, when the Invid Regess and the rest of the Invid transcended their corporeal forms and left the earth, both Sera and Ariel were left behind.
Sera continued to live with Lancer after the war, although Lancer made sure to keep it a secret, even from reporters. In 2044, they were living in a cottage and Sera was expecting a baby. (Robotech: Love Live Alive!)