Which honorific is used to address a married woman in English-speaking countries?

TRUE CANADIAN Laurel, Canada is in America, North America

TRUE CANADIAN Laurel, Calm down, mellow, no reason for this. As the explanation stated American English or British English (which would be, as you stated, The Queen's English) is equally represented & acknowledged here. Yes, there are many places in the universe that English is spoken, however, the Q/A/E with this specifically singled out the two as American English & British English.

"Mistress" used to be a very honourable title, but now it has changed its meaning.

Mrs derived from the contraction Mr's, i.e. belongs to Mr.