I have a friend who does that too!
The Miss Firstname thing is common here mostly among very young children. My sons preschool teachers were referred to that way, and my daughter's Girl Scout leaders were when they girls were in Daisies and Brownies. Beyond that they called them by their first names only. That is not taken as a sign of disrespect here so long as the child knows the adult "well," or even if they just met the adult, so long as the adult introduced themselves that way. The kids normally follow the lead of the adult on that, whether calling them by first name, Miss Firstname, or Mrs. Lastname. Mrs. Lastname is almost exclusively reserved for teachers at school or church.
I also wonder, whether it is really "regional" or not...how many here refer to people to their face as Aunt A, Uncle B, Cousin D, etc as adults? Very few people that I know do that. Most will say "my Aunt A" when talking about them, but drop the "Aunt" when talking to them. I have one niece from NJ that calls me "Aunt Michelle" (she's in her 30s) and it always strikes me kinda funny. I also have an elderly cousin from Alabama who will call and say, "This is Cousin June." Also strikes me funny.
And one more: I had a coworker who referred to his parents by their first names. It seemed odd and disrespectful to the rest of us. Someone asked him about it one day and he said that his parents are from Norway, and they do not find it disrespectful at all. (
According to him, I claim no knowledge about this at all) He said that to them it is odd for an adult to say "Mama" or "Dad," that is only expected from children. If I referred to my father by his first name, I think he'd come unglued.