When she receives her final wages, contact the Revenue and request that your rate band be set at €51,000 with credits of €5,625 (including married and PAYE credits).
Request that they apply the 'Week 1/Month 1' basis. This will ensure that her allowances are maintained for the entire duration she is not working by you
Once she returns to work, she should call the Revenue and revert her rate band to €42,000 with €3,750 in credits, resuming the standard week1/month1 basis.
She will then continue to utilize these allowances for her employment.
By doing this, you will have benefited from the higher allowances while she was not working and prevent liabilities in a tax return and it will minimise your tax situation on wages during the year in real time