I don't know what you mean by already taxed. If you are the beneficiary, you inherited the IRA. If you withdrew some or all of the money, you will owe income tax in the year of the withdrawal. You might have had taxes withheld from the withdrawal, but the withdrawal still needs to be reported on your return, and you get credit for the withholding, but you may owe additional tax if the withholding was not enough.
If the IRA had no beneficiaries, then it went to your parent's estate, and was paid to the beneficiaries of the estate. Most of the time, this is the same as I mentioned above, you get an IRA, and if you withdraw money, you owe income taxes. Rarely, the estate will pay the income tax, and you just get money that is not reported on your tax return. If you believe the estate paid the tax, you should confirm that with the estate administrator. Normally, you inherited the IRA, and will get a 1099-R for the money you withdrew.
