There is no gift tax in Canada. Neither the giver nor the receiver have to pay tax on a gift (unless it's from your employer or something similar). There are a number of rules around income attribution preventing couples from doing unauthorized income splitting, but none of them apply here.
You can pay whatever expenses of your wife's you like. You can pay her income tax, or you can give her money that she can put into her RRSP, whichever you prefer. You can pay her credit card bill as well, whatever is on it. Unless you are gifting property or something similar there will be no tax consequences. Of course you won't reduce your own income tax bill - your income is still your own.
With some couples only one partner has income, and they pay all the expenses for their spouse. This doesn't result in any extra tax liability. (It doesn't reduce tax either).
Also, rather than allowing her to pay into her RRSP, consider contributing to a spousal RRSP. You get to claim the refund (which will be higher than hers if you are paid more) but you have to have spare RRSP room yourself.