If you're married and your wife's income is low relative to yours then perhaps you should assign all tax credits from your wife to you (please ask in the tax forum as I have no real idea how that works in Ireland).
If you own the property then the rental income is due to you. If your wife gets the income then it is a gift from you but there is no gift tax between spouses in Ireland as far as I know. It would presumably have to be income taxed first before you gave it to her as a gift but as above, you'd have her tax credits anyway.
I stand to be corrected on all this, just throwing it out there.