The Mary that I referred to was a possible match for her mother.
I think the Mary that I found in 1911 is the widow of a John or Patrck Shea and not Thomas.
It does appear that quite a few Shea's appear in the poor house records.
The couple that I found in 1881 has Thomas occupation as labourer and they were living in Ward 4, District 9, city of Halifax and it doesn't give a street.
You can access McAlpine's and Hutchesons City Directories for Halifax through the site at Collection Canada or try and internet search for Canadian Directories - Who Was Where.
McAlpines directory 1881 Halifax
has
Shea, Thomas - custom Boot and Shoemaker, 53 Barrington St., Home - Argyle St
Shea, Thomas - night watchman, 5 Lower Water St
Shea, Thomas - labourer, h. 199 Albermarle St
Shea, Thomas - tinsmith, h. Richmond St
When you go to the census info, almost all of the Shea's are RC and originate from irish origins. The library in Halifax may be able to give you info on how to find the most likely RC church in this area of Halifax. All of these streets are in the same area of Halifax, close to the harbour.
It is entirely possible that they moved accomodations often. There isn't any census information readly available before 1881 so looking through all the bmd's for a connection to Thomas and Mary may be the only way to find any info on your Mary Shea's siblings.