Hi Elizabeth
I found a Martha Bolton in Wooler:
1841 age 50 Innkeeper HO/107/833 12 30 7
1851 age 64 Proprietor of houses b. Wooler HO/107/2422 413 23
This Martha seems to be about 10 years older than the Martha who was living with Edward in the 1861 and 1871 censuses and was probably born at Wooler not Howick. In 1841 she had just a maid in her household and in 1851 she was living alone. The 1851 census entry shows her as unmarried.
If Martha became a little confused with age then Edward might have guessed her birthplace and age for the censuses and death registration. However, Freebmd has the death of a Martha Bolton in 1854 (Oct - Dec 1854 Glendale 10b 205) so it is possible that there were two elderly and unmarried Marthas in the area but I can only find the one in the 1841 and 1851 censuses.
Ancestry's search seems very unstable just at present, possibly because they are getting ready to change the way it works and it may become easier when they have sorted all the bugs out. I got as far as I did by searching the British census collection for Martha Bolton, born in England, Northumberland 1895 +/- 5. When Ancestry told me she could not be found I just made it try again. Sometimes, when I had just looked at an image and returned to search results the original results had disappeared but I could get back to them by repeatedly pressing the browser back button.
It's difficult to know what to do to try to resolve some of the questions raised by these elusive Boltons - I think that I would be tempted to get the Margaret Henderson marriage certificate in 1857 and also to get the death certificate for the Martha who died in 1854 but this would be a gamble and you could end up no further and having spent £14.
All the best
Gobbo, who rushes in where angels fear to tread!