That looks a really good match except Grace's DOB is out by a few years.
Grace was shown in the 1851 census as aged 36, and in 1861 as aged 46. That tallies
exactly with a birth in 1814/5. Griz(z)el and Grace, for reasons I have never quite understood (they have completely different origins), are treated as interchangeable names in Scotland. I wouldn't worry about spelling variants - any version of G*ll*n could occur. So I think that this Grizzel Gillon looks like a pretty good match for Grace Gullan or Gullen. (The village of Gullane in East Lothian is pronounced Gillon.)
Bear in mind that ages in the 1841 census are supposed to be rounded down to the nearest five years. So if Grace was born in 1814 she could have been 26 or 27, but she would have been listed as 25. If you then subtract 25 from 1841 you get the wrong answer anyway, because the census was taken half-way through the year, so half of the population had not yet had their birthdays in 1841, and consequently show up as born a year later than the actually were born if you 'calculate' their DoB from their age in the census.
Ages in 1851 were supposed to be exact. So if there is a disparity between the age in the 1851 or later census and the age on a death certificate, I tend to think that someone who is alive is more likely to know their own date of birth than someone who is registering the death.
