Hi rochs
It used to be the case that these might have been exempt in Ireland.
Depending on the amount and whether your wife ever got a previous inheritance would be two factors. If it is taxable, she should be able to get a deduction in respect of US tax paid. The rate is 20%.
I assume that the allowance for your wife is because she did not qualify for a Contributory Pension. Therefore the allowance that you got would have been means tested.
The long and short of this, if she keeps the money, and if it is over €20k, the they would seek to reduce the amount as her 'means' would have changed.
I dont have a lot of details to go on, so maybe some advice is needed.