Statutory death registration started in Ireland in 1864, so if Mary Breslin died in 1871, aged 85 or thereabouts, there ought to be a death certificate for her. There won’t be one for her husband if he died in 1860. Inver falls within the civil registration district of Donegal town. According to rootsireland, there is a Mary Breslin death registered there on 5.4.1871 aged 80. She lived in Drimareeny, parish of Inver and was a farmer’s widow. The informant was Francis Gallagher, of the same townland.
Looking at Griffiths Valuation for that townland in 1857, there was 1 Breslin farm, held by James Breslin. He had plot 4 which was a 10 acre farm. It’s possible her was Mary’s husband. The townlands more common name is Drumrainy.
No Breslins there by 1901, though the Gallaghers were still there:
The RC baptisms & marriages for Inver don’t start till 1861 so you won’t find any baptisms or marriages for the family.