Susan and Mrs. Elliott are in a carriage after delivering Christmas presents to neighbors and friends.
Suddenly, Mrs. Elliott accuses Susan of making all of the decisions in her marriage. For example, she claims that Oliver doesn't have any interest in this whole cement business.
Susan defends herself, arguing that she and Oliver make their decisions as a couple. Furthermore, she's the one who's paying rent, which is evidence that they have a fairly equal relationship.
Upon hearing this, Mrs. Elliott says that "it's worse than [she] thought" (3.4.34).