So, her basic pay from work was reduced by the amount of the mat ben? (ie gross pay reduced from 600 to 330 and a further 270 paid to your wife by social welfare). If this was the case then no tax or prsi would have been operated on the non-taxable pay and so no refund would be due.
A refund arises when the employer continues to pay the usual 600 gross and the mat ben is paid over to the employer but tax operated as normal.
It is something of an anomaly that a person in receipt of mat ben or the first 6 weeks of illness benefit is actually better off after tax than they normally are.
Sybil