You can avail of the full 'married two incomes €64,000 income tax band' at 20% if you transfer the title to the rental property into her sole name.
If there is a mortgage on the property, you will need to first contact your lender to see if they have any objection to a 'joint mortgage, sole title' situation. If they agree, you can then contact your solicitor to transfer the property to your wife's sole name.
The rental income would then become her only source of income and would be taxed, after deductions, at 20%.
There are also no tax complications as asset transfers between spouses are exempt from tax.
Make sure you get a fee estimate from your solicitor before proceeding - we did this last year and paid €450.00.