The gift is above the threshold for declaring a gift as it exceeds 80% of the current threshold for Category A, Parents to child of € 335,000
She will have to declare the gift using form IT38
The Capital Acquisition Tax is based on the cumulative total of all gifts received since Dec 1991.
If has received any prior gifts and the total exceeds € 335,000 than she will be liable for tax at 33% on the amount above this threshold
This the tax position for Ireland
I do not know if there are any tax implications from a UK point of view