In the earlier part of the novel we read that Manon admires her father in the way he treated his slaves, which is opposite of how her husband treated his slaves. However, toward the end she calls her father a hypocrite and place a picture of him face down. What changes or thoughts caused Manon to think differently of her father at the end?

In Valerie Martin's novel, Property, the slavery period of the United States is examined, and particularly the dynamics between the slave owners and the slaves. The main character of the novel, Manon, is the daughter of a plantation owner in Louisiana. She admires her father despite the fact that he owned slaves. The beginning part of the novel showed how people of that era were blinded by what they considered social norms.
Figuratively speaking, Manon is still "asleep" during the beginning of the story. When she marries a man who also owned slaves, she is repulsed by it, and yet she still admired her father based on memories of his good qualities. In essence, she disliked her husband for his perversions and sociopathic behavior, and therefore it was easier for her to point out his immoral acts of enslaving other human beings.
On the other hand, she was, at first, able to brush off her father's similar acts of atrocities because of surface-level fondness for him. When a slave rebellion kills her husband and leaves her destitute, she has a psychological and spiritual awakening. This event triggered her consciousness to admit that her father was just as complicit in the crime of slavery as her former-husband.