Marie, wife of Augustine St. Clare and mother of the angelic Eva, is a hard-hearted, selfish hypochondriac. Once the belle of the local ball, she is completely incapable of human sympathy, especially toward black slaves. She barely notices her daughter’s fatal illness. She’s also reluctant to think hard about anything if it might cause her the slightest inconvenience to do so. Her favorite thing to do is keep the entire household up all night with her petty ailments and needs. St. Clare keeps her cruelty toward the slaves in check to an extent – he won’t allow her to send them for public whippings and beatings – but she is a harsh, demanding mistress.
When Augustine dies, Marie shows her utter indifference toward the fate of her slaves. She sells them all at the public auction block, despite the fact that it was her daughter’s dying wish and her husband’s intention to free Tom, and despite St. Clare’s determination to dedicate himself to abolition. When Ophelia tries to remind Marie of these obligations, she has a convenient fit of illness.
Like Simon Legree, Marie St. Clare is an extreme caricature of a villain without a conscience. But unlike Legree, Marie isn’t cruel with the object of making a profit or working her slaves efficiently. Marie’s housekeeping is so neglectful that St. Clare must bring his cousin, Miss Ophelia, down from New England in order to run the estate and look after his daughter. In Stowe’s opinion, a Victorian woman who can’t manage the household finances and servants is neglecting her primary duty.
Ironically, the slaves in the St. Clare household consider it "proper" for a genteel southern lady like Marie to stay entirely out of household affairs. Ophelia’s attempt to control household expenditures and oversee the servants and their activities seems "unladylike" to them. This is Stowe’s hint that the high culture of the South, especially in the way it relies on slavery, interferes with the contributions women should make to society as wives, mothers, and housekeepers.