Well, nothing really jumps out at me with this one, but could be around 1905 or so. The sea of fog they appear to be immersed in obscures the length of the lady's skirt and her shoe style unfortunately

What an odd portrait style...it might be a copy.
Is the back a postcard? If so could you please show the back, could be a very important dating clue.
The high collar on the lady had been going for quite a while but started disappearing just before the war. She seems to have the puffy blouse front that began in early Edwardian era but faded out maybe around 1910ish. Her hat is rather narrow...hates got wider and wider until about 1911 when they started getting smaller again.
So. That's what I can tell you regarding style/year A/year B etc

What I
can't tell you is how long a lady might have worn a favourite blouse even if it was out of style, or because the family had fallen on hard times and she had to wear clothing a decade old. Older ladies felt more comfortable in older clothing that they were used to. Lots of factors that you just can't pin a value on. There are some hard-and-fast date points, such as a particular style of shoulder seam that began in the year 1889 and was never seen before that....but for the most part dating is more art than science

Cheers,
China