Mardola is the main antagonist of the Stargate Atlantis episode "Harmony".
She was portrayed by Crystal Lowe, who also played Vala in Smallville.
History
Mardola is the older sister of Harmony and Flora. In 2008, she requested Lt. Colonel John Sheppard and Dr. Rodney McKay to escort Harmony to the Ruins of Larris, as she was next in line to become Queen of the Pegasus Galaxy after their mother passed away.
However, she had other intentions. Mardola was secretly employing the Genii to capture Harmony, because she believed Harmony was too young to be Queen. However, with Sheppard and McKay as escorts, Harmony eluded capture.
After the beast, actually Ancient Mini-Drones killed several Genii, the capture order turned into a kill on sight. After they escaped and returned to the castle, they discovered a Genii communicator in her quarters. Harmony then banished Mardola to a prison until she would be "Too old to be remember".