Jane Smith marries John Doe and keeps her name, and doesn't adopt her husband's.
It seems a good conclusion of this question that it's simplest/best to refer to her as Ms. Smith.
I'm curious if it's improper to refer to her as Mrs. Smith.
My instinct is that "Mrs." implies something like "Smith's wife," but am unsure.
Of course, it'd be ideal to simply find out from her her preferred term of address, but I have in mind the context of addressing a stranger who I happen to know is married and kept her family name.