Teres

If we assume she deliberately chose to use the modern 'tea' instead of the medieval 'tisane' - which is a very big 'if' - I personally would consider it an understandable concession to readability.

That said, I'm inclined to think you're right about her having just been careless and thoughtless, it's just that as a Catholic I am required to be as fair and charitable towards everyone as I can.