Sorry, I ought to have given more information about the family. This family has six generations of women called Euphemia, so it is confusing at times.
Euphemia Bell's mother was Jane Bell (1844-1893). Jane Bell's parents were Colin Bell and Euphemia McDougall. Jane's mother is with the family in the 1841 census, but she is not with them in the 1851 census, so she may have died sometime between 1841 and 1851. I found a burial record for a Euphemia McDougall in 1847, which may be her. It is from the OPR, so there isn't much information. Colin's death certificate indicates that he was a widower, so his wife has died by 1857.
Euphemia's mother Jane married John Laidley in 1870, about 7 years after her daughter was born. Jane later married Donald Campbell after John died in 1884.
Rosie17, you are correct; this Euphemia Bell is the one who married James Irvine.