On the basis of having a photograph where the woman, my grandmother, is dressed in a very similar fashion I would say it will be before 'the 1920s'. My mother who was born in 1916 used to be upset, as a child, when she saw the similar photograph, as she was not in it. She was told she was in it but was hiding so well that she could not be seen. The photograph I have which is similar was Edwardian ie 1901/10
The woman does not to be in her 40s, to my eyes she looks younger.
The child in the dress may not be a girl. Boys and girls were often dressed in similar fashion, though perhaps the socks and shoes may be girls? Babies at this age are very difficult to 'sex' from photgraphs but when I first looked I thought it was a boy.
Also a tip, we often want to slot people into the families we have heard of, with the family members we have heard of. Deaths in childhood were sadly a fact of life in those days so a family that we think we 'know' now had say, two boys, may turn out to be another family altogether who had two boys who grew to adulthood but lost several children in their early years.
There will be other, more expert daters......coming along I am sure.
