First on why "Madame Le Ferre" may be used: (Wikipedia)"It is normally impolite to address people by their given names unless one is a family member, a friend or a close work colleague of comparable hierarchic importance. One also does not address people by their last name only unless in a work environment. Also, contrary to English or German usage, it is considered impolite to address someone as Monsieur X when talking to that person: a mere Monsieur should be used, Monsieur X being reserved for talking about M. X to another person.
When speaking of someone, Monsieur/Madame given name family name, by far the most polite form of address, is generally reserved for the most solemn occasions. (HEY LOOK!!!!!)Monsieur/Madame family name or given name family name is polite and used in normal formal occasions, as well as in the formal quality press (Le Monde, Le Monde Diplomatique, for example).
By contrast, in colloquial usage the family names of personalities are used alone. Formally, a married or widowed woman can be called by the given name of her husband (Madame (given name of husband) family name or Madame veuve (given name of husband) family name); this is now slightly out of fashion.
In the workplace or in academic establishments, particularly in a male-dominated environment, it is quite common to refer to male employees by their family name only, but to use Madame or Mademoiselle before the names of female employees.
and naming practices: Wikipedia: "Since the 1789 Revolution, the law stipulates that "no one may use another name than that given on his birth certificate"; furthermore, the 1946 revision to the Constitution guarantees that "women and men have equal rights", including in the use of their birth name.
Upon getting married, a woman keeps her maiden name (nom de jeune fille). She may, under her maiden name, for example, open a bank account, sign cheques, obtain a passport, etc.
However, marriage grants a married person the right to assume his or her spouse's last name. It is still a common practice for a woman to use her husband's name in this way, despite the fact that no official due process formalizes this usage.
(HEY LOOK!!!!!)The majority of married women use their husband's name for all documents, official or not. The article 264 of the French civil code does, however, stipulate that "upon divorcing both spouses lose the right to use each other's name".