Donald is surely a separate Scottish name? Any Dónals I know use Daniel in English if they're using a different name for English; this is the norm in Ireland.

To complicate things, O'Donnell, in Irish, would be Ó Dhomhnaill, or son of Dónal.

The Greek king's daughter may very well have a subsidiary meaning in 17th- or 18th-century Irish; many confusing-in-English terms do.