@ pinkprincess
Here is what I have found about the Catherine Main who I think is your ancestor. Don't worry about the discrepancies in her year of birth. This was quite common and also, I suspect, Catherine was trying to make out the older she got the younger than she actually was!!
In 1871, aged 9, she was in East Street, South Shields with parents Thomas nad Mary Ann and siblings Thomas, Marion and Isabella.
In 1881, aged 19 and a milliner, she is still at home with parents and the 3 above siblings plus 2 more William C and Cairns. Father is a tailor and the family are now living at 18 Ocean Road, Westoe.
In 1891 the parents are now at 32 34, James Mather Terrace, Westoe with Marion, Isabel and Cairns and they have 2 more children and Jane K and Frances C. Frank Main, described as grandson and aged 5, is also in the household.
Catherine is working as a nurse in the home of a Thomas (a master mariner) and Isabella Hunter at 2 Eleanor Street, Westoe. Her place of birth is given as South Shields and her age as 25 (giving approx date of birth as 1866).
In 1901 father, now a widower, is at 30 George Scott Street with 4 of his children.
Catherine is now a cook domestic at a boarding school - 2, 4, Percy Lodge (Harrogate Ladies College), The Oval, Harrogate. Age this time is given as 32 making year of birth approx 1869 and place of birth as South Shields.
In 1911 Thomas is still at the same address as in 1901 with various children and grandchildren.
Catherine in now a housekeeper in a drapery house (looks like some sort of hostel for drapers' assistants) at 59 & 61 Granger Street, Newcastle-upon-Tyne. She is still described as single, aged 44 (giving approx year of birth of 1867) and place of birth as South Shields.
I've found a marriage between a Catherine Main and a William B Hemsley registered in Morpeth district in Apr-Jun 1911 and then the death of a Catherine Hemsley aged 60 registered in Newcastle-upon-Tyne district in Jan-Mar 1925.
Birth of William Brewis Hemsley was registered in Morpeth district in Jan-Mar 1887 (making him about 20 years younger than Catherine!). He was son of Thomas and Mary Scott Hemsley (per census 1891). In 1901 he was at boarding school in Barnard Castle. By 1911 census, aged 24, he had his own farm at Bockefield Felton, Morpeth where he was living with just a housekeeper. His death was registered in Northumberland Central district in Oct-Dec 1945.
I'm fairly confident this is your great grandmother and step great grandfather but the only way to prove it is for you to send off for the marriage certificate between Catherine and William in 1911. If you do, please let me know the outcome.