A few things incorrect here.
Ireland is not in the Schengen area, so a Schengen visa is useless to gain entry to Ireland.
Even if the Thai citizen is married to an Irish citizen. Financial proofs are still required, along with proof of return (flights), insurance etc.
This is because there is no “marriage visa” in the irish system for short term visits, so the applicant has to apply for a standard short stay tourist visa.