If the daughter of a duke or marquess or earl who bore the courtesy title "Lady Mary Smith," married Mr. John Jones who was subsequently knighted by the Queen, would she continued to be called "Lady Mary Jones" or would she be called "Lady Jones" by virtue of her husband's being Sir John Jones?With courtesy titles there is a difference between those who possess the title birth and those who acquire it by marriage.
I will offer Lady Helen Windsor as an example. As the daughter of the Duke of Kent, she is entitled to the courtesy title of 'Lady'. When she married Timothy Taylor, she took his surname and became Lady Helen Taylor. Now if Timothy Taylor were to receive a knighthood, she would still be Lady Helen Taylor because her courtesy title as the daughter of a Duke, outranks her husband's knighthood.
Another example would be the late Diana, Princess of Wales' sister, Lady Jane Fellowes. When she was born, her father was Viscount Althorp and she was known as The Honorable Cynthia Jane Spencer. Upon her father becoming Earl Spencer in 1975, she became The Lady Cynthia Jane Spencer (though she prefers to use her middle name). When she married, she took her husband's surname and became Lady Jane Fellowes. Her husband, Robert Fellowes, was knighted, but this did not change her title, as the daughter of an Earl, this again outranked his knighthood.
However, in 1999, Sir Robert Fellowes was granted a Life Peerage and became Baron Fellowes, of Shotesham in the County of Norfolk. When this happened Lady Jane took the style Baroness Fellowes, or more informally Lady Fellowes, which, believe it or not, is actually a demotion as Baron is the lowest rank of the peerage and Lady Jane is the daughter of an Earl - one of the top three peerages.
Now, in the reverse, when the husband is given a knighthood, the wife is entitled to be known as Lady (husband's surname). An example of this would be Paul McCartney. When he was knighted, his wife took the courtesy title Lady McCartney - at the time this was Heather Mills McCartney. She could not be known as Lady Heather McCartney because she took the title from her husband instead of her father. Unlike Lady Helen Taylor, who takes the title from her father instead of her husband.
© Marilyn Braun 2009