Initially, Dana doesn't hate Rufus at all. They first meet when he is a young boy and drowning in a river. Dana saves him, which creates a bond between her and this young child. As he ages, Dana recognizes the impact Rufus's father and his society have on him, and she sympathizes with him to a point.
Yet eventually, Rufus becomes a grown man who is responsible for his own actions and choices. The hope she initially holds for the man Rufus could become erodes as she watches him exert his will over the slaves on the plantation. She must learn to suppress her growing hatred of Rufus, particularly as his intentions toward Alice and even Dana grow increasingly vile. In this historical context, Rufus holds all the power, and Dana must make impossible choices day after day in order to survive.
When Alice kills herself, Dana's anger toward Rufus grows. However, she tries to use her connection with Rufus to convince him to free the children he fathered with Alice. In navigating this request, Dana demonstrates the ability to put the needs of Alice's children above her own need to vocalize her hatred of this man.
After the funeral, Dana again attempts to use her position to convince Rufus to free all of the slaves on his plantation in his will. He doesn't agree but doesn't immediately oppose the idea, either. Again, Dana is willing to suppress her own vehement objections to Rufus's choices in an effort to make life better for others.
Dana suppresses her hatred of Rufus for so long because he often feels "like a younger brother" (chapter 4) to her. As a Black woman who is treated like a slave in this historical context, Dana certainly feels intense bitterness toward this man who is despicable toward her and others based solely on race. Rufus feels that he is superior to Dana, and he ultimately attempts to physically prove this when he attempts to rape her. She finally recognizes the futility in believing that suppressing her true feelings will ever make Rufus evolve into a better man, and she sinks her knife into his side.