Nan is a common alternative or nickname name for ann or annie etc in Scotland so will probably be the same in ireland
Queen Ann was known as Brandy Nan as she was fond of a swally! Burns song "My Nanie's Awa!"Skoosh.
Like Queen Ann, known as Brandy Nan as she was partial to a dram. I say partial........ Skoosh.
Sometimes used for Agnes also, & mebbes a wee bit auld-fashioned, the new Royal Bank of Scotland fiver features the author Nan Shepherd! Skoosh.
Anne/Ann/Annie/Nancy/Nan/Nanny/Agnes/Hannah, etc. are all different forms and can be used interchangeably.