Do you have her actual marriage certificate? If not, that is your first step. It will tell you the exact date and place of the marriage, and the maiden surname of her mother.
There is a death of Christina Robertson or Malcolm, aged 58, in Edinburgh in 1948. Her death certificate should also confirm the maiden surname of her mother.
If she was 58 when she died in 1948, she would have been born in 1889 or 1890, not 1894. So it looks as if one of the ages listed is inaccurate.
There are 14 births of Christi* Robertsons in the City of Edinburgh between 1889 and 1894.
Unfortunately the only marriage of a John Robertson before 1889 seems to be in 1856, which is surely too early to be the correct couple.
So it is possible that John and Bridget were married outside Scotland, perhaps in Ireland, or that they were not married at all.
There isn't a Christi* Robertson listed with a Bridget on the same census page in 1891, 1901 or 1911 anywhere in Scotland, though it's possible that they could be on different pages
To get those certificates go to
www.scotlandspeople.gov.uk, invest in a few credits at modest cost, and you will be able to download them for less than the cost of a cup of coffee each. See what they tell you, and then get back to us with that information.