This might be a possibility for you, nkiaora:
The 1877 marriage registration between Robert Stevenson and Grace Dunlop gives her father's name as James Dunlop. On Oct. 15, 1904 there is a marriage registered between a Grace Dunlop, age 60, WIDOW and a John Coile both from Carnageeragh, Parish of Loughguile, Ballymoney. All Saints Church, Church of Ireland. The interesting part is that Grace Dunlop, WIDOW, gives her father's name as James Dunlop. If this Grace is a widow and James Dunlop is her father, then who was she the widow of? (I guess that it's Robert Stevenson but more proof is needed.)