This question is asking about a very brief exchange between Isabel and Lady Seymour that happens in chapter 36.

The chapter begins with Lady Seymour in ill health. She is not doing well, and Madam Lockton tries to convince the doctor that Lady Seymour should return to Charleston to fully recover from her illness. The doctor strongly disagrees and believes that the journey would kill Lady Seymour. Isabel believes that is Madam Lockton's actual intention. The solution is that Isabel would tend to Lady Seymour while she is bedridden and in ill health. During this time, Isabel makes repeated trips to the prison to visit Curzon and bring him food. Conditions at the prison are bad. Prisoners are "fed," but they are fed with food that is often rotting.

Isabel takes to saving some of her own food to take to the prison as a way of solving this problem. Lady Seymour is an observant woman and notices that Isabel saves food that isn't being eaten. At one point Isabel stresses that Lady Seymour needs to eat to keep up her strength, and Lady Seymour responds by letting it be known that she knows that Isabel takes her extra scraps to the prison. Lady Seymour thinks it is the "fine and Christian" thing to do; however, she warns Isabel that Madam Lockton might not see it that way. Lady Seymour knows that Madam Lockton is a harsh slave owner, and Lady Seymour warns Isabel that returning to the prison might earn her painful repercussions from Madam Lockton. This is a legitimate warning, as Madam Lockton is a woman that isn't averse to branding Isabel and trying to sell off Ruth simply to spite Isabel.