Unfortunately that is not going to be an allowed deduction for you if it was not actually classified as alimony. Child support payments or any other type of payments which you are required to pay on behalf of your former spouse that are not designated as alimony are not deductible. The IRS does not allow taxpayers to claim a deduction for the federal taxes they must pay on their income, so they are also not going to allow anyone else to claim those taxes as a deduction just based on the fact that were paid for a third party.
However, I would suggest that you double check what your are being asked to pay in taxes for her. Assuming she is filing as a single person with no dependents, then she could have income of up to $43,300 for the year before she would ever hit the 25% tax bracket. And even then the 25% would only apply to the earnings over that amount.
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