Thank you for this advice - the articles on researching Irish records will be very useful.
Catherine's siblings are older than her, the names I know of are Mary, Eliza and John. I have the marriage certificate for Catherine, married 1873 in Liverpool - her father's name is Robert O Gorman (deceased by this date) and profession given as butcher. No idea of her mother's name or where she was from.
Will follow some of the research guidence and see what else I can find out about Robert O Gorman.
Many thanks
C