What cause the argurment at the end of chapter 7?

The subject of marriage makes things tense. Mother starts asking more  questions about Mrs. Ogilvie's sons. At one point Jeannine snaps that, "Mrs. Cook is asking if you might consider Miss Cook as a wife for one of our brothers. And I imagine their filthy little tavern is part of the deal." Mattie feels deeply hurt by this insult and verbally attacks Jeannine. Mother tries to diffuse the argument before punches are thrown.