That marriage was registered in Mitchelstown, Co Cork, not in Co Armagh. Mitchelstown 1876 Volume 19, page 393. I suggest you send for that marriage cert and get Catherine’s fathers name and address from it.
You can order a photocopy from GRO Roscommon for €4 per certificate. Put the place, year, quarter (where there is one), volume & page number on the application form (anywhere). http://www.groireland.ie/
You have to post or fax the form to them but they will e-mail the copy certificate to you if you wish. Put “please e-mail to…..” clearly on the top of the form.
Tradition was to marry in the bride’s church (assuming the couple attended different churches) so that may be the place to look for the bride’s baptism and that of any siblings. Unless it was a registry office marriage, the church will be on the certificate.