What is Madam Lockton like?

I'll start with something fairly tame. Madam Lockton is a wealthy woman who is also a British Loyalist. That's about the nicest thing that readers can say about her.
She's a slave owner, unkind and unfair. She makes it her personal goal to find ways to hurt Isabel. Madam Lockton is also fully capable of hurting Isabel in both physical and emotional ways. At one point in the story, Madam Lockton gives a severe beating to Isabel, who bravely takes the beating in Ruth's place. Later, Madam Lockton has Isabel branded on the face with the letter "I" for insolence. To hurt Isabel emotionally, Madam Lockton lies to Isabel and tells her that Ruth has been sold to another owner. Chapter 43 has a great quote that shows what Isabel thinks of Madam Lockton.

Everybody carried a little evil in them, Momma once told me. Madam Lockton had more than her share. The poison had eaten holes through her soul and made room for vermin to nest inside her.

Madam Lockton is a greedy and selfish woman, and she takes out her anger and frustrations on other people. This occasionally comes back at her in bad ways. Her actions feed her husband's temper, and he is a violent man himself. Often their fights become physical, but Madam Lockton is so rotten to the core that it is nearly impossible to feel any sympathy toward her.