Mrs. Slade and Mrs. Ansley don't agree on much. There is so much tension there, and the one thing they do agree on (Babs is the more vibrant and beautiful of their daughters) is a source of tension since she isn't Mr. Ansley's daughter but Mr. Slade's.
The collective idea of modern mothers would not include sitting on the veranda crocheting or knitting and staring out over the city as if they were old and had one foot in the grave. This is the view of them that their daughters have as they trip along down the stairs to a city full of life and entertainment.
Since both Mrs. Slade and Mrs. Ansley are sitting there basking in the tension years of jealousy creates, perhaps they do also agree on this view as well. They are both content to be in each other's company in order to finally get things off their chests, but they would not categorized themselves as "not modern"--especially Mrs. Slade who is so caught up in the "in thing". From Mrs. Ansley's actions, words, and thoughts, we get the impression that she is not so concerned with what others think about her...she is the not the "keep up with the Joneses" type.