I just double-checked the online 1881 Census listing and AIRTH doesn't appear as a 2nd name for Catherine ~
Gregor MCINTYRE, JR.MMaleScottish27OntarioFarmerPresbyterian Margaret MCINTYREMFemaleScottish27OntarioPresbyterian Jessie A. MCINTYREFemaleScottish3OntarioPresbyterian Gregor A. MCINTYREMaleScottish2OntarioPresbyterian John Henry MCINTYREMaleScottish<1 Born: Sep; 6/12OntarioPresbyterian Gregor MCINTYRE, SR.MMaleScottish72ScotlandPresbyterian *Catherine MCINTYREMFemaleScottish55ScotlandPresbyterian Catherine MCINTYREFemaleScottish70ScotlandPresbyterian
Source Information: Census Place Horton, Renfrew South, Ontario Family History Library Film1375870 NA Film NumberC-13234 District113 Sub-districtB Page Number10 Household Number38
Perhaps the Catherine that Gregor Sr was married to as of 1881 was a Catherine who just happened to be born the same year!
I do know that I saw a little booklet many years ago that had Gregor McINTYRE Jr as the son of Catherine AIRTH ....