This is the pub...
There is a Black Horse Inn still open at Spennymoor.
The Black Horse Inn in Tudhoe / Spennymoor
There was a Black Horse Farm there.
Then a colliery, known at the time as the Black Horse Colliery
The Black Horse Inn dates back to the same time as the colliery, opened in the 1860's
John Kirtley was living at Tudhoe Colliery in the 1871 census.
I don't know what happened to his wife Jane.
There seems to be no birth registration for the daughter Jane, age 1 month in that census (nor has a baptism been found)
Her age pretty much matches Isabella's age in the 1921 census, 50 years and four months.
I guess John and his wife settled on Isabella for her name, rather than Jane.