There is a marriage for Eileen* Morrin in Ballinrobe Dist 1947 to Thomas Omalley the online view certs dont show up to 1947. There are 2 births to Morrin/Omalley in Ballinrobe Michael 1948 and Patrick 1949.
The graves you mentioned address Togher which is in Hollymount Dist plus she died after 1996 which again seems to be another clue. I have looked at the Newspapers for all the names and dates on the graves for an obituary but cant find any.
If you google Michael Omalley Togher Hollymount there is a death notice for a man died 2004 died Luton from Togher, the age is 66 which matches 1948 birth, sadly only his own family mentioned no sibling or parents.