You say that Sarah was born in 1868. However the only Coppals-Black marriage I can see was in Greenock in 1881. If Sarah was born in 1868, then she was only 13 when she got married. That doesn’t seem very likely. Do you want to revise her year of birth? Have a look at her marriage certificate or the 1881 or later Scottish censuses to get her age from that.
Also, Scottish marriage certificates record both parents names, and occupations. So can you let us have that information?
I suspect Sarah was born before 1864 which is when birth registration started in Ireland. So to trace her, we need her religious denomination. The marriage cert should tell you the denomination of the church they married in. What was it?
I suspect the spelling of her name in Ireland will be Cupples. Quite a common name in Co. Antrim.