Pearlina, my Atlantean OC,  is the protector of the Mother Box of Atlantis.  It is her responsibility to make sure that the Mother Box does not get into the wrong hands.  However, when the box cracks, and Steppenwolf comes for it, she does her damned best to make sure he doesn't get it.  Aquaman also comes to assist in stopping Steppenwolf, but both of them are unsuccessful.

Arthur tells Pearlina that he has been invited to create a League of heroes on the surface world, and she should join, because he is contemplating joining as well.  Of course, she says yes, and joins Arthur for the cause to stop Steppenwolf once and for all.