I wasn't going to weigh in but you made me

Yes, it's what a younger person calls an older person to avoid the familiarity of just "L" but soften the formality of "Ms Florida". Courtesy in the south is very ritualized and in many ways reflects the caste system we still live under in some places. It is something we pride ourselves on, southern hospitality, although it can be as fake as can be.
To hear an older person address a younger person as Miss Nancy is just strange and wrong to my ears and it jolted me. If Nancy called her Ms Neves ahe should call her Ms Grace in return but the Ms Nancy came across as a deliberate attempt at ingratiation. And it probably was just that.
I would like to know if Mark N (love his name!) is still spokesman or whatever for Theresa.