So I googled this question, and here's what this other site said:

"Federal estate taxes are not deductible, but state inheritance taxes are deductible on your federal taxes.Enter the amount on Schedule A. You will enter the amount of line 8, which is "Other taxes." You will also need to write that the amount is a state inheritance tax. This amount will be totaled up with all your other deductions and be used to reduce your taxable income. This, in turn, reduces the amount of federal income tax that you will owe." The site is called Sapling

So this would be a huge deduction for my client. It's contrary to the link you found.