Aquawoman

Nothing is yet known about the woman referred to as "Aquawoman." She was a prisoner of the World Army, held in statis in the Black Basement of their Arkham Command Center. (Batman/Superman #1)

When that facility was attacked by Superman, Batman appeared intent on freeing two key allies, one of which was she.

When she was released, Batman bowed to the sea queen without hesitation, addressing her as "majesty." This seemed to pacify her as Batman moved on to free his next target: Jimmy Olsen. Upon seeing the queen, Olsen referred to her as "Aquawoman," which she hastened to say was a nickname she abhorred. (Earth 2 #18)

She introduced herself as Marella, the queen of Atlantis and helped the others locate one of the World Army's secret prisoners: a Kryptonian named Val. She had the strength to punches through the concrete floor, and then withstood the full brunt of a plasma cannon. (#19)

The group escaped into the air with a lift from Hawkgirl. It might have been considered "out of Marella's element," but with her control over water, she harnessed the vapor in the clouds and drowned a legion of Parademons. After this, she was intent on returning to Atlantis but vowed to help when called. She gave Batman a shell with which to call her. (#20)

Notes

A stasis chamber bearing the name "Aquawoman" was first seen in Batman/Superman #2 (Sept. 2013).