Final answer:
The given texts do not contain enough information to specify which historic event Mrs. Croft keeps bringing up, and a definitive answer cannot be provided without further context.
Step-by-step explanation:
The historic event that Mrs. Croft keeps bringing up is not explicitly provided in the given texts.
However, the passages contain various historical and conversational elements that suggest events occurring around the turn of the 20th century and dealing with matters such as World War I, property and marital relations, and societal roles.
Since there is no direct mention or clear context of Mrs. Croft's repeated references to a specific historic event, a definitive answer cannot be provided based on the provided information.
As such, it's important to refer to the full text from which the question is derived for a comprehensive understanding of the historic event Mrs. Croft may be fixated on.