For what reason did Esther kill her father in the novel, This Other Eden?

When Esther was still a young woman, her mother died. Her father then began to sexually abuse Esther's sister, Abby. To escape their father, Abby fled the island. After her departure, Esther's father began molesting her as well. Esther soon discovered she was pregnant by her father.

On the night that her son Eha was born, Esther sought to kill the child. She took the newborn down to the river and considered what it would mean to drown him. Before she could do so, however, Zachary Hand to God Proverbs found and delivered her. He brought her and the baby back to her house and ensured they were okay. Not long later, Esther found her father sitting on the edge of the bluff after Eha had fallen asleep. Because of the violence he had subjected her to, Esther pushed him over the cliff to his death.