I think this is why Martha was working as an Umbrella Maker on the 1851 census
From Directories
1818
John Dodson, wood turner, Cheapside
1821 and 1830
Umbrella makers
John Dodson, St Martins Lane
Umbrella stick makers
John Dodson, (and walking) St Martins Lane
1849
John Dodson, Umbrella and...