Why does Prue state that she would rather go to “torment” than to heaven? What new “horror” of slavery is revealed by Prue’s life story

Prue makes this statement because she'd rather not end up in heaven is that's where the Master and Missus are gong to be. Heaven doesn't sound like a good place to her, if her earthly misery is going to be there.

"I looks like gwine to heaven," said the woman; "an't thar where white folks is gwine? S'pose they'd have me thar? I'd rather go to torment, and get away from Mas'r and Missis. I had so," she said, as with her usual groan, she got her basket on her head, and walked sullenly away."

Prues' horror came when she was tending her sick mistress, who refused to get milk for her baby when all of the stress of caring for her dried up her milk. The horror was that children were left to die without a second thought.

"But Missis tuck sick, and I tended her; and I tuck the fever, and my milk all left me, and the child it pined to skin and bone, and Missis wouldn't buy milk for it. She wouldn't hear to me, when I telled her I hadn't milk. She said she knowed I could feed it on what other folks eat; and the child kinder pined, and cried, and cried, and cried, day and night, and got all gone to skin and bones, and Missis got sot agin it and she said 't wan't nothin' but crossness. She wished it was dead, she said; and she wouldn't let me have it o' nights, cause, she said, it kept me awake, and made me good for nothing. She made me sleep in her room; and I had to put it away off in a little kind o' garret, and thar it cried itself to death, one night. It did; and I tuck to drinkin', to keep its crying out of my ears! I did, -- and I will drink! I will, if I do go to torment for it! Mas'r says I shall go to torment, and I tell him I've got thar now!"