I've stated Newport is in California, but with the mobility people in the US have, only 48% of adults living in California were born in California (real-world data). Meemaw and Betty were born in Jackson, MI, grew up in Atlanta, and Meemaw moved to California, and Betty to Africa (several countries). I guess that Norah using some southern word wouldn't be out of place because her mother and aunt could have used it. And that, by imitation, can move down to MC/The girls' generation.
It's the same with this gesture
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I reserve it for the family and, occasionally, Eileen. Is everyone Italian? Nope, but Olivia and Betty use it, it passed down the generations and Eileen has copied it unconsciously. You won't see any of the students using it (before the epilogue)