I might be able to simplify this for you, Prof. Sometimes you need a linguist (albeit in my case an amateur one) rather than a historian.

Moira is indeed neither Irish nor Scottish. But the reason people associated it with the Gaelic countries has to do with Anglicization of Gaelic names. The original Irish name that acquired the spelling "Moira" is Máire. This is a variation on Muire, the Gaelic name for the Virgin Mary. In Irish tradition, "Muire" is reserved for her, while the similar sounding "Máire" is used for other Marys.

To my ear, Máire is pronounced /'mɔɪ̯ːɹə/ , which is more or less equivalent to the middle and final syllables of "Palmyra", and not too different to the typical pronunciation of Moira.

The question is whether the spelling is legit within your story, and that comes down to period. I think by the late eighteenth century Anglicized names were fairly common in Ireland, but I'm not sure exactly when the shift began. Medieval Ireland certainly would be too early for English spellings.
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Regards,
Eric Fretheim
Assistant Prep Leader, 2015 October NaNoWriMo Prep Challenge

"It is perfectly okay to write garbage-- as long as you edit brilliantly." ~C.J. Cherryh

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