Sorry, missed the important bit in the OPs question re the Qualified Adult! You're correct Sally, the Qualified Adult is means-tested, even though the pensioner is claiming on PRSI contributions.
From welfare.ie
Any income your adult dependant has from employment, self-employment, savings, investments and capital (for example, any property except your own home) will be taken into account.
Your income is not taken into account, only your spouse's or partner's income is taken into account, in the assessment for a Increase for a Qualified Adult. If you have joint savings or investments etc., only half is taken into account as belonging to your spouse or partner.
The cut-off limit at the moment is €300 per week - if income is assessed as over that amount, no qualified adult rate is payable.