The bomb that falls and temporarily knocks Bendrix unconscious acts as the "act of god" that brings Sarah to feel that there really is a god. She sees Bendrix lying there and assumes he is dead or dying and prays fervently, promising to give up all the bad things she does as well as her relationship with him if god will only allow him to live.
As he rises, in Sarah's mind from the dead, she vows that she will in fact give him up and when she has the chance she breaks things off with him. So she reveals that she has decided that god does exist and that she believes that he listens to prayers and interacts with humans on the level that they can make deals with him, etc.
In the end, her belief in god drives her to run from Bendrix and she struggles to make sense of a god that would allow for such painful struggles. In the end she cannot allow the real happiness of a relationship with him to enter her life and she dies of pneumonia, caused by her continued flight from him in the rain and sleet.