“Defiant”…Interesting editorial choice for a woman insisting that her marriage was quite valid. Henry’s actions merely showed himself a serial adulterer. Defiant might describe him, but not Katherine. She was the victim here and Sir Thomas More, friend of Henry, lost his life standing up for that same truth.
You seem to be thinking of some ideal "correct" state to defy.
Not to knock your personal beliefs, but Henry VIII was head of the country and the country was England so that made him the head of the church, too. There was nothing greater to defy than the king.
So the cypher contains 'Katherine', there is evidence that she herself spelled her name with a 'K', as the article mentions, but then they refer to her as 'Catherine' throughout, even directly after talking over this point.
My history teacher shared a great quote from a royal matriarch in Denmark at the time, who was asked if she'd consider becoming the next wife of Henry VIII.
"If I had two heads, I'd happily put one of them to the disposal of the king of England," she'd replied. "But as it is...."