The author favors Mrs. Ansley over Mrs. Slade. Both women are equal socially, financially, but Mrs. Slade is bitter. Mrs. Ansley is sympathetic, genuine and sincere.
When the discussion turns to their trip to Rome when they were young, Mrs. Slade thinks that she has the upper hand, in a snide sneering kind of way. She wants to hurt Mrs. Ansley. Mrs. Slade is unhappy with her life.
Mrs. Slade thinks that she is in control of the situation, having written the letter to her friend, she thinks that she fooled her into waiting, and waiting for the man she was engaged to. Now Mrs. Slade is bitter and looking to put Mrs. Ansley in her place once and for all.
But it is Mrs. Ansley who has the most surprising news to tell. She is the more sympathetic character of the two. I think that the author favors her, Mrs. Slade wants to hurt Mrs. Ansley.
Then Mrs. Ansley tells Mrs. Slade the truth about her tyrst with Delphin,
"Mrs. Ansley had not moved for a long time. But now she turned slowly toward her companion. "But I didn't wait. He'd arranged everything. He was there. We were let in at once," she said." (Wharton)
Mrs. Slade still feels smug, she says,
"At the end of all these years. After all, I had everything; I had him for twenty-five years. And you had nothing but that one letter that he didn't write." (Wharton)
Then Mrs. Ansley says, I had Barbara.