The unnamed Abbess runs the Red Cathedral of Mechanicsburg, and is clearly a member of a very Militant Order of Clergy. She wears a red veil and surcoat over white leggings and a white wimple (nun's head and neck covering), black cavalry jackboots, and a Greek cross with a trilobite on it at her throat. She wields a cutlass or falchion, left handed and edge up.
She first enters the story on page 126 of volume 12 ✣ , during the Siege of Mechanicsburg; she is in the Cathedral displaying anger with Moloch von Zinzer's roving work-party for their supposed damaging of the structure via a mechanical squid/narwhal battle. When convinced the problems are not of the group's origin, she calls for her charger, and tells her staff to see if Moloch and his crew can get the Bloodstone Paladins running and "equipped for sustained smiting."
Her behavior later ✣ essentially confirms that she is a part of The Storm King conspiracy. She appears with the now-functioning Paladins and greets newly-arrived Martellus von Blitzengaard as the new Storm King. As he leads the Paladins into battle against Baron Wulfenbach's forces, the Abbess seemingly mistakes Agatha for Zola (explicitly dismissing the fact that Castle Heterodyne has recognized her as a true Heterodyne), and attempts to take the "fake" prisoner and lock her up in the Cathedral until needed. Moloch knocks her unconscious and she is hauled away by Cathedral staff.
Following the breaking of the siege, Tweedle says she was the one that called ✣ him to Mechanicsburg. When he kidnaps Agatha and takes her into the depths of the Cathedral, the Abbess is waiting for them and helps him escape ✣ Mechanicsburg with Agatha using the Monolith, though in the general confusion of that exit she gets pretty badly clawed up by Krosp, and then is left behind in the time-frozen city.