My ancestors hailed from Ireland but I have no idea what parish ?

My grandmother, Catherine O'Shaughnessy, was born in Ireland.  I believe it was in the 1890's.  She and her sister Anne came to New York as teenagers.  I am now sure of the name of their parents, but my Uncle said they had a brother named John who died in a car accident in Ireland.  My uncle always said his mother was from County Cork, but I have learned through research that might be where they left from and not necessarily where they lived.  I also found some things that led me to believe she might actually have been from Limerick.  I don't know what else to do.  I am planning a trip to Ireland, but that's not for a couple of more years. I do think it's possible that her father's name was Patrick.  It would make sense to me because my father's middle name was Patrick.  Any help anyone could give would be greatly appreciated.