I am sure Mary Cain is not in any elite shape anywhere fast enough to be competing for the Irish. She very likely got advice from her ultra-wealthy family's advisor at BBR wealth management, who also just so "happen" to be Mary Cain's main sponsor at Atalanta NYC. Evan Roth is the CEO of BBR wealth management and is the head board member of Mary Cain's whimsical Atalanta NYC.
With switching allegiance and the Irish tax system, the goal is to avoid paying American taxes to the IRS by claiming income is earned in Ireland even though you live in America, have no job in Ireland, and rarely if ever step foot in Ireland. You basically register a shell company in Ireland and then have all your American income and "donations" go to that Irish bank account owned by the shell company you control. As long as Mary Cain claims the American money was earned by the Irish shell company and she doesn't try to move the money back to an American bank, she pays no American taxes. And she will pay very little tax to the Irish because the rates are so low over there.
With all that American money laundered to an Irish shell company, you can then do what all ultra-rich people do and launder it further to other shell companies to make "investments".