It's a pity that death certificates don't give much information.
It's going to be difficult going back that far.
I looked at Griffiths for Cunninghams in Killasser and Attymass parishes but there are none

As we can't see a marriage in England, and Winifred was born in Alnwick c 1850 (do you have her birth certificate?) you are looking for a marriage c 1848/49.
If there are 2 Farrell Ruanes in Griffiths as appears to be, one of them- Killasser parish is presumably the one born c 1820 and dies in Swinford district 1882.
He may be married to Honor McNicholas according to FS.
Then there is one who is married to Bridget Deacy in Foxford (Toomore) having children c 1865.
Also a Martin Ruane, married to Bridget McNulty, having a child, Farrell in Ballina area c 1870. Possibly Attymass?
Not sure what any of this indicates but it often helps to go over these things.

Attymass/Killasser and Toomore civil parishes all border on each other
