Cheers MyLuck for the extra info.
I never knew about the brother MICHAEL. Also to say, the daughter MARY A, must also have died as Patrick and Catherine had my Mary on 16th July 1882! Would it have been unusual to re use the same name?
I got my church marriage record for them from ROOTSIRELAND.
15th July 1868
Parish/district of BALLYBRACK.
PATRICK MASON to CATHERINE DOYLE (was she widowed)? both of LOUGHLINSTOWN
Husbands father PATRICK MASON Wife's father JAMES MASTERSON
Patrick from KILGUADE Catherine from BALLYBRACK
Both mother's are un-recorded.
Witness 1: Mary Mason
Witness 2: Simon Brian.
Also, here is the headstone erected by Esther Mason in RATHMICHAEL old cemetery
http://www.igp-web.com/IGPArchives/ire/dublin/photos/tombstones/dublin-rathmichael-old/target26.htmlAs you said, it seems odd that neither marriage is listed anywhere. I know from relatives still living, she was very religious, so would expect everything to be above board!
The search continues!

P.S. I also have from ROOTSIRELAND a baptism cert for CATHERINE
No date of birth recorded.
Baptism 29th March 1846
Parish district of BOOTERSTOWN BLACKROCK and DUNDRUM
Father JOHN MASTERSON (on marriage cert it is JAMES)
Mother MARGARET (surname not recorded)
Sponsor 1: Patrick Tanner
Sponsor 2 : Ellen Hugues