As the wife of a British prince, she takes his name.
Catherine, Duchess of Cambridge is legally Princess William, Duchess of Cambridge.
Therefore, Princess Michael’s husband is Prince Michael of Kent. He is the grandson of Queen Elizabeth II’s grandfather, George V, and the Queen’s cousin due to the fact that her father, George VI is Michael’s uncle.
Therefore, she is Princess Michael of Kent.
OK...I don’t know about that. Of course the chances of me ever addressing them is about the same as Floridians in Key West celebrating a White Christmas... :-).