In the Southern US, "Miss" is used colloquially as the feminine equivalent of "Mister", regardless of marital status. It is prefaced as a courtesy title, usually when the woman is somewhat older than the speaker, or when the social distance is just close enough to know her given name, but not close enough to allow you to refer to her solely by that name, e.g., "Miss Mary", "Miss Ethel", and so on. It's a hard thing to describe, you just kind of sense when to use it.
It is yet one more example of the genius of Southern speech, as in using "y'all" to denote a plural "you", something that is missing from standard English.
I’m from the northeast, but after my Dad was stationed in the south before I was born, he and Mom thought the “Miss” address followed by the first name was perfect for addressing people for whom a first name alone, “Seraphina” was too casual, but the full address, “Miss Scanlon” was too formal. “Miss Seraphina” was perfect, for, say, your babysitter or close family friends who were adults or significantly older than oneself. For males, we used “Mr. + first name. “Mr. James” was what we called our trash man, not “Mr. Green.” My Dad knew him from the Navy where he was cook on USS St. Paul. However, my parent’s friends who were married, and with whom my parents were close friends as a couple, became technically unrelated Aunt and Uncle, their children were Cousin. So we had Aunt Maryjane, Uncle Phil, parents to “Cousin” Marjorie, Kevin, Julie, John, and Dave.
I still like this custom, so while I’m on first name basis with my best friend who is from West Virginia, I’m called ‘Miss ‘Phina” or “Auntie ‘Phina” by her adult children and grandchildren. I call her adult male children “Mazter Alan” address pronounced that with a z and barely discernible r on the end. Male grand or great grandchildren are “Nephew” or “Niece.” All newborns through maybe age two are “Baby.”
After the birth of a child, or if the person is single beyond their mid-forties, they become “Cousin.” It sounds complicated, but it is really just what seems natural and respectful.