I hate to disappoint you but it has no Irish Gaelic spelling. In fact it's not even Irish: it is a Welsh name, a pet form of Margaret. It's original spelling is Megan [meg-an]. I suppose it's similar to Caitlin/Katelyn: an American phenomenon. The "name books" used in the USA are full of misinformation. The closest Irish name would be Peig or Peigín.
With the accent marks: Írusán [eerusaun] in Irish.
In Irish Gaelic: an oiche. (Accute accent on i) In Scottish Gaelic: an oidhche
There is a Gaelic website translator that will teach you to say it in Gaelic or you can just say it in English with an Irish accent and for that I recommend Boondock Saints
In Scottish Gaelic: fìrinn (mind that the accent is grave, not acute like in the Irish)
gach rud everything In Irish
Be aware that 'Gaelic' is actually two separate languages: Scottish Gaelic (called 'Gaelic' in Scotland) and Irish Gaelic (called 'Irish' in Ireland).In Irish: gadhar rua or madra rua (the latter can also mean 'fox')In (Scottish) Gaelic: cu ruadh.
The Irish Gaelic translation for Daddy's Girl is Peata Dhaidi
Is mo chuid den tsaol thú
Íocfaidh mé as gach rud.
Irish: f-yunn (N & W) f-yoon (S) Scottish:
Brotherhood before everything
I will pay for everything.