The Duchess of Cornwall uses her title instead of what other title, the title held by the first wife of Prince Charles?
Camilla, Duchess of Cornwall:  Instead of using the title of Princess of Wales, she uses the title Duchess of Cornwall, her husband's secondary designation. Princess of Wales: Princess of Wales (Welsh: "Tywysoges Cymru" ) is a British courtesy title held by the wife of the Prince of Wales, who is, since the 14th century, the heir apparent of the English or British monarch.
Princess of Wales