Yes that was the one.
I've explored the possibility that she remarried - potential in 1906? But again I can't be sure as I can't verify other facts to conclusively say yes or no to this possibility.
This one?
June 1906 Easington 10a 961
Harrison, Sarah Jane
Nicholson, Robert
+ 2 others
1911 in Shotton
https://www.familysearch.org/ark:/61903/1:1:XWHQ-S9C
I think there's a very strong link with marriage and 1911 census.
In 1901 census Sarah Jane Houston has a 10 month old daughter called Maggie, born Houghton Le Spring. In 1911 census Sarah (Now Nicholson has a 10 year old daughter Margaret Nicholson born Houghton Le Spring.I reckon Margaret has adopted the Nicholson surname.
HARRISON, MARGARET -
GRO Reference: 1900 S Quarter in HOUGHTON-LE-SPRING Volume 10A Page 506
SS
added
The 1911 census gives an address of --12, Fifth Street, Horden, Shotton, Durham, England
Fast forward to 1921 census-12, Fifth Street, Horden, Shotton, Durham, England
Robert still at this address with a "different wife" but a son Edward who appears in 1911.
So either Robert/Sarah have parted or she has passed away.
Possible remarriage of Robert Nicholson.
Marriages Sep 1919
King Margaret Nicholson Easington 10a 1255
Nicholson Robert King Easington 10a 1255