I don't recall Nat making any comment about Granny Shepard being a laundress/mangler, however dee-jay, you are correct that she is listed as one in the 1851 census. I suppose it is possible that this is something she took up after 1846 to make ends meet.
1851 census
Tottenham Court
Strand Union Workhouse
Mary Shepard, wid, 80, mangler b Warwickshire, Birmingham
(There are 26 pages of inmates in this institution)
1851 census
27 Stephen Street
Cock Family
John Burns
Mary Elizth Kennington, unm 63, mangling, b Middlesex, St James Piccadilly
Ann Fox, 49, Charwoman, b Middlesex, Queen St
Nov 20th 1851
Parish of St Pancras
Mary Shepard buried, age 80, abode: InfirmaryThere does seem to be some manglers within the circle of friends/family, so I would say any lead on Ann Fox would be worth chasing up.

I would think that many of these women's occupations would be interchangable eg charwoman/mangler? Also thinking about a couple of the gifts that Ann gave Nat - a handkerchief for example, may have been pilfered from the laundry basket. Jumping to conclusions here of course, but stranger things have happened.

I also loved Nat's 'Sunday' entry - with the precise details about the coffin etc.