Here "strong" represents "stubborn." A "strong face" means a stubborn expression on a person's face. This implies that the woman is acting in a stubborn way, that she is deliberately doing what she knows is wrong. Alternate translation: "with a shameless expression on her face" (See: [[rc://en/ta/man/translate/figs-idiom]] and [[rc://en/ta/man/translate/figs-metonymy]])