Mary McDowell’s marriage in 1872:
https://civilrecords.irishgenealogy.ie/churchrecords/images/marriage_returns/marriages_1872/11321/8154426.pdf
I can see Agnes & Isabella in Jaffa St in 1901 and in 1911 but cannot identify Agnes after that. It is such a common name that it will be very hard to trace her without some clues. I don’t see birth certificates for either Agnes or Isabella and suspect they may have been a bit older than they declared in the 1901 census. Their ages in 1911 point to births in the 1850s.
Elizabeth McDowell appears to have died in Belfast on 13.7.1885. Husband Benjamin had pre-deceased her. Her age is given as 53 but that’s probably out by a good few years, if she had a daughter in 1850. She was probably nearer 60.
https://civilrecords.irishgenealogy.ie/churchrecords/images/deaths_returns/deaths_1885/06280/4799439.pdf
I cannot find a death for Benjamin 1864 – 1885 which suggests that he died before 1864 (when death registration started) and that reinforces my suspicion Agnes & Isabella were older than they said in the 1901 census.
1911 census here:
http://www.census.nationalarchives.ie/pages/1911/Antrim/Shankill/Jaffa_…
Family were Church of Ireland and place of birth is given as Antrim. Could mean Antrim town. Antrim town Church of Ireland baptism records still exist and a copy is held in PRONI in Belfast. If you are looking for birth records that might be worth a look. Might also give you Elizabeth’s maiden name.
Benjamin & Elizabeth look to have married before 1845 when statutory marriage registration started.
I searched for deaths in Belfast up to 31.12.1921 (which are free) but did not find Agnes. You could search the deaths on the GRONI site 1922 onward but at £2.50 a time it could be expensive.
