Based on the narrative at the beginning of Chapter 9, how does Penny's mother's relationship with Mr. Mulligan become more apparent to Penny upon her return home from Nonny's?

Based on the narrative at the beginning of Chapter 9 of the book, the relationship that Penny's mother shares with Mr. Mulligan is becomes more apparent to Penny upon her return home from Nonny's through her mother's actions, which include her mother no longer lying to her, but simply telling her that she is getting dressed to go out dining and dancing with Mr. Mulligan.