I would start by looking at the 1856 marriage certificate. Catherine is indexed under “Cath.” Place of registration is Moyle. Tradition was to marry in the bride’s church (which should be on the certificate, unless it was a Registry Office marriage). That church may be the place to look for her baptism and that of any siblings. You can view the certificate on-line on the GRONI website, using the “search registrations” option:
https://geni.nidirect.gov.uk
(You will need to open an account and buy some credits. It costs £2 to a view a certificate).
The certificate should give you her townland and father’s occupation which may enable you to identify that family in Griffiths and earlier records eg the tithes and the 1803 agricultural census, and Rev Traill’s 1803 census of Ballintoy. (The Steel family might also come from Toberkeigh as I see a Robert Steel, blacksmith, living there in 1803).
William & Catherine had 12 children, 11 of whom were still alive in 1911. Catherine herself was still alive in 1901:
http://www.census.nationalarchives.ie/pages/1901/Antrim/Croagh/Toberkeigh/922620/
and in 1911:
http://www.census.nationalarchives.ie/pages/1911/Antrim/Prolusk/Toberkeagh/113898/
What may be her death was registered in Ballycastle on 17.4.1927 aged 88. Again you can view that on the GRONI site mentioned above.
I noted this probate extract for a Robertson from Toberkeigh. The full file should be held in PRONI in Belfast:
Robertson John of Toberkeigh Bushmills county Antrim farmer died 27 September 1958 at Route Hospital Ballymoney county Antrim Probate Belfast 7 January to Alexander Edward Martin solicitor. Effects £1353 11s. 5d
A Steele farm in Ballintoy in 1901:
http://www.census.nationalarchives.ie/pages/1901/Antrim/Croagh/Toberkeigh/922613/
In Griffiths Valuation, James Robinson senior and James Robinson junior are both recorded as farming in Toberkeigh in 1861 (Robertson/Robinson are interchangeable as surnames). Adam Steel is also recorded as farming there that year.