The CGT calculation goes like this :-
Original Cost £ 8,200 in 1989 is indexed up using the revenue table
If purchased before 6th April 1989, multiply by 1.553
If purchased on or after 6th April 1989, multiply by 1.503
Remember, the Govt cancelled the indexation in 2004. And the indexation had nothing to do with the real rate of inflation - it was just a mechanism to alleviate some of the inflation.
Assuming purchased after 6th April, restated cost = £ 8,200 x 1.503 = £ 12,324
Convert to euro = £ 12,324 / 0.787564 = € 15,648
Capital gain = 45,000 - 15,648 = € 29,532
Your parent will get relief for the portion of time the lived in the house as a PPR plus last 12 months - so that would seem to be about 20 years out of 21 ie 20/21 * 29532
so the relief would be about € 27,954 leaving a taxable gain of
29532 - 27954 = 1,578
Less annual CGT allowance of 1270 or twice that if house was owned jointly - not necessarily the case.
I don't know where you got the figure of 6,000 from but it's clearly wrong or else the amounts and/or dates you've given are different from the ones used to calculate the 6,000