Just found it:
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You will be considered a dependent spouse if:
you are dependent on your spouse;
you have a gross income of 76.18 euro or less per week;
your income exceeds 76.18 euro per week and you were dependent on your spouse before entering or resuming insurable employment (at Class A, E, H or P);
you are not getting a social welfare payment (except Disablement Pension, Supplementary Welfare Allowance, or Child Benefit);
you are getting a Carer's Allowance or Old Age (Non-Contributory) Pension in your own right and were dependent on your spouse immediately before receiving Carer's Allowance or Old Age (Non-Contributory) Pension.
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These are the only grounds. I do find this all a morass of clauses and subclauses. I'm going to see if she'll qualify under some other scheme....