If the person was employed by the health board/HSE, and the employer was topping up the state maternity benefit. I believe there is a section on the MB application form, if the woman wants the MB paid directly to her employer.
This is quite normal in many PAYE jobs - the employer pays the salary as normal and it is taxed in the normal way (as if the employee was still in work). Employee fills in a form which entitles the employer to receive the maternity payment directly from SW (to reimburse employer for paying it as part of "salary"). Employee then seeks a tax assessment at the end of the tax year for reimbursement of overpaid tax as the MB portion of salary that was paid is exempt from tax.
In reply to other posters, Revenue can only go back e.g. 25 years, in cases where they suspect tax fraud i.e. a criminal offence, has been committed. I think they can only go back 6 years for normal audits.