She was introduced as a woman who loved her husband and wanted nothing more than to bring their son back to rebuild Daxam; unfortunately, when Mon-El chose Kara and Earth over his parents and Daxam, Rhea… didn’t take it so well, murdering her Herculean husband and deciding that she would take her son back, even if that meant taking Earth.
Rhea used the portal to bring a Daxamite armada through space to Earth for an invasion, and Kara is in serious trouble now.
Supergirl introduced a brand new baddie in Season 2 with Queen Rhea of Daxam.
She made an alliance with Lena Luthor, and in “City of Lost Children,” we discovered just what they were working on: a portal.