What does Irene regret not saying to John when she ran into him?

Irene regrets not telling him the truth.

Irene was thinking: "I had my chance and didn't take It. I had only to speak and to introduce him to Felise with the casual remark that he was Clare's husband. Only that. Fool. Fool." That Instinctive loyalty to a race. Why couldn't she get free of It?