Given your mention of Rose Devlin (as a witness to Lizzie McMullan's 1900 marriage), I briefly rooted around for a McMullan-Devlin angle and in so doing happened upon a transcript of a marriage for a William McMullan and a Catherine Devlin in 1856 in Duneane RC church. This couple went on to have children baptised in Duneane RC parish: Thomas bap. 1857, John bap. 1864, James bap. 1866, Nathaniel bap. 1869, William bap. 1871
, and Elizabeth bap. 1874 - I struggled to find any associated civil birth registrations, maybe someone else with fresher eyes can.
But the only reason I mention this at all is that the stated address in the last two baptismal records (William in 1871 and Elizabeth in 1874) was the townland of Muckrim, which borders Millquarter...
https://www.townlands.ie/antrim/toome-upper/duneane/muckrim/
Do you think this is a possibility?
I have just obtained a copy of the church marriage records for Elizabeth ( Lizzie) McMullan to John Murray. It states that Elizabeth’s mother’s name is Catherine nee Devlin. This means that gaffe was correct from the start. I am now finally sure I am at last on the correct course. Thanks again gaffe and all.