Miss Mary Finch was one of the more humane slave owners.  This makes her different from other slave owners in the historical context of Chains.  

One way in which her views differed from those of other slave owners is in her actions before her death.  When she dies, her will orders Isabel and Ruth to be freed from slavery: "Ruth and me are free, Pastor. Miss Finch freed us in her will. Momma, too, if she had lived. It was done up legal, on paper with wax seals."  This is vastly different from other slave owners, who would simply transfer slaves like property.  The attitude of Robert Finch, the nephew who wants to take control of Isabel and Ruth despite the will, is reflective of the standard slave owner.  

Mary Finch was also different from other slave owners in the way that she interacted with slaves.  Isbael remarks how she would say "please" and "thank you" when assigning them work.  She also taught Isabel how to read. This was "odd" behavior when compared to other slave owners.  Mary Finch's humane treatment of slaves distinguished her from other slave owners. 

The fact that Robert asserts such quick control and the Pastor does not object despite the will represents how different Mary Finch truly was from other slave owners.  The slave-owning society could not comprehend her demeanor and actions.  Even though she does not grant freedom to Isabel and Ruth while she is alive, waiting until death to do so, it is evident that Mary's actions and attitude toward her slaves was contrary to the standard practice of the time.