Ernestina was the only female member of the Stackpoole family. Due to a bizarre mutation she and her three twin siblings (Myron, Otis, and Weeler) were born their own unique ability. Her ability is to sap the wills of men. It is unknown if these abilities could be applied to females as well. Unfortunately this same mutation caused her to veber develop a mind of her own and instead be subservient to the will of her brother Myron. She uses her ability several times in the couse of the film. The first is to lure to her so Otis can knock him unconscious. She uses them again to force Lance into having sex with her, a fact which is later used agianst him. Finally she draws Lance closer so Otis can attack him.
She is last seen bending to the injured body of myron, seemingly prepairing to help him to safety.
At the end of the film it is implied that Myron survived. If this is the case it is likely that Ernestina survived as well.