Hi Mel,
Cannot help with Mary Ann's birth

Have found an appropriately aged Mary Ann in 1841 as follows:
62 Bridgegate, GlasgowJames Stewart, 39, Shop Keeper, Ireland
Mrs Stewart, 39, Ireland
Elizabeth Stewart, 15, England
Mary Ann Stewart, 11, Dressmaker, England
James Stewart, 78, Ireland
What a shame it says Mrs for the mother! Have you considered looking at the death entry for Mary Ann Rae, as this will give details of her parents. (If she died in Scotland that is!)
Also with regards to the above census, it may be worthwhile to look at Elizabeth, i.e. whom she married and track her through the censuses to see if it gives her a birth place of Hull and of course if you found her marriage entry it would give parents details.
Have tried to find Mary Stewart born c1807 in Ireland on the 1851 census, but to no avail!
Kath