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I'm not sure this is the best place to ask this — if you're looking for a trope to match, Trope Finder or the Trope Talk forummay be a better place for that.
But with regards to the original query, I don't think "Margaret Ann" signifies a particular place in the Anglosphere. Attaching Ann to the first name sounds somewhat antiquated, but it's not uncommon nor tied to a geographical location.
(I've coincidentally edited the work's page to adhere to TVT formatting and indexed the page. Just don't forget to crosswick your examples).

Hi I'm created a page for the 1985 action-adventure series Lime Street that is mostly remembered for being a Non-Actor Vehicle for child peace activist Samantha Reed Smith who played the elder daughter. By the way, the younger daughter character is "Margaret Ann" rather than just Margaret. Is that meant to demonstrate that they live in Virginia?
https://www.youtube.com/watch?v=rMuwcSiqTxU
https://tvtropes.org/pmwiki/pmwiki.php/Series/LimeStreet