I have not been able to check the details in the original publication. The version I've inspected was reprinted in Georgette Heyer: A Critical Retrospective, ed. Mary Fahnestock-Thomas (Saraland AL: Prinny World Press, 2001): 461-472.
"In the context of 1940, Pen's assumption of a masculine character posed little danger to the established order. However, for the female reader of the time and/or the would-be wartime volunteer, Pen legitimises difference, exceptionality, and the desire to function in a male world. But the limits to female aspiration are clearly defined. As a boyish woman, Pen is marked out as praiseworthy because she achieves the virtues of an average, unexceptional boy and, within a system of values which views men as superior to boys as well as women, there is never any danger of her competing with or equalling grown men. [...] It is important to note that this is not a fixed scheme throughout Heyer's work." (467-468).