After Frances gives birth to Hareton, the doctor says she will die soon of consumption (what is today called tuberculosis). There is no hope for her to survive.
As Nelly tells the story, the girl who usually brings breakfast when she and the other servants are helping with the hay comes running out early to see her. She tells Nelly that Frances has just given birth and is filled with joy, but that the doctor says that now that her pregnancy is over, there is
nothing to keep her, and she'll be dead before winter.
As it is June, this gives Frances about six months to live. The girl also tells Nelly that she will be the one to care for the baby and help raise it after Frances is gone. Nelly is to feed it with milk and sugar, which implies that Frances cannot nurse it. The girl tells Nelly that she is envious of her, because the baby will be like her own child after Frances is dead.
Nelly will indeed become the nurse and surrogate mother to Hareton, but Frances's death will drive Hindley into grief, rage, and alcoholism, tearing apart the family.