Although old Mrs. Dubose is highly critical of Atticus and both of his children, she has nothing bad to say about Jem's and Scout's mother. Atticus's wife died from a heart attack when Scout was still a baby, and Mrs. Dubose remembers that "A lovelier lady than our mother never lived." Mrs. Dubose thought that Atticus should have remarried since it was "heartbreaking the way Atticus Finch let her children run wild." Jem's reaction to the sick, old lady's remarks?
... he went livid when Mrs. Dubose shot us this message. (Chapter 11)
Jem later took out his anger on Mrs. Dubose's prize camellia bushes, but it was her remarks about Atticus "lawing for niggers" that was the final straw.
(These quotes can be found on the second page of Chapter 11, page 100 in my old paperback from 1982.)