Further thanks to arryboy (not forgetting 'er indoors) and Jimsgirl. All four members that have made suggestions have helped so much and I cannot thank you all enough.
My mind is so much clearer now, and I have basically made up my mind as to who my mystery lady is. However, just for further thoughts, here are two later in life photographs of the people who are the two persons I am trying to tie the original photograph in with, and here are some details about them so that the sleuths amongst you might like to add additional thoughts, given the timeline and facial likenesses (if any).
Both were born in Greenwich/Woolwich, Kent UK
Charlotte Atwater was my great grandmother, born in 1866. The photograph attached now was taken in 1917 so she would have been about 51. She was married at the age of 17, and had her first child, a son, when she was 23.
Mary Charlotte Evans was Charlotte's daughter, my grandmother. This photograph was taken just prior to her untimely death a few months later. She was born in 1887 and her first born son was not born until 1909.
Cheers and again, many thanks, Diana