I really couldn’t say. It’s beyond me and she will not post on any message board despite my attempts to get her to post here.
I will say she is a purist of sorts when it comes to language. She fully understands that words and language evolve over time but she views this evolution going backwards and diluting the language. Muddying the pool, so to speak. And that upsets her (figuratively).
As a way to address people goes, without asking, I think she would default to the situation. Is it a formal event or people at a friend’s house having a party? Teacher Susan Smith might be Ms. Smith in the classroom but Susan at the back yard BBQ.