ammack: I was the one who looked up the census information, not scottishmisty who started the thread. You can find out about Catherine's daughter by looking up the census.
The 1861 census has:
South Boisdale Mr McLellan's, South Uist
John McLellan farmer of 21 acres age 49, born South Uist
Mary McLellan wife age 40, born South Uist
Catherine McLellan farmer daughter age not transcribed or entered, born South Uist
Margaret McLellan farmer daughter age 17, born South Uist
Donald McLellan scholar age 14, born South Uist
Catherine McLellan scholar age 14, born South Uist
Malcolm McLellan scholar age 9, born South Uist
Catherine Morrison formerly ag lab age 90, mother in law, born South Uist
A bit odd that there are two daughters called Catherine - could be an error, but I'm only going from the transcription of Ancestry. Be worth looking at the original on ScotlandsPeople.
So according to that, Catherine had a daughter Mary born in about 1821 at South Uist who married John McLellan.