The following excerpt comes directly from gradesaver, and the link is included in the sources below;
Dual Identities
"There is an odd dynamic between England and France that dominates the novel -- the former is depicted as a land of justice and simplicity and order and propriety, whereas the latter is vulnerable to the impulsive rage of mobs and sacrificial violence. As a result, then, Marguerite/Lady Blakeney comes to serve as the perfect symbol of this schism. As Marguerite, she caused the condemnation of the St. Cyr family simply through a misspoken denunciation. Upon marrying Percy Blakeney, she maintains her French casualness -- her haughty charm, but her innate ability to hurt people without thinking. Through the course of the novel, she turns more and more English, evolving gradually into the true Lady Blakeney, who stands by her husband, humble and deferential."
Hopefully this helps a little.