It's hard to be completely exact when it comes to photos of people outside of studios, because they may not have been planning to be photographed and therefore wearing clothing that's out-of-date or having their hair not fully styled. That being said, there are certain clues here.

The woman's dress is pre-1901, because it lacks the blousing in the front of the bodice that is characteristic of the early 20th century. The high collar could have been worn any time between about 1883 and 1908. Her sleeves are fitted through the arm, all the way up to the shoulder, which means that they may be from any point in the late Victorian era except, roughly, 1889-1897. Her hair lacks bangs (fashionable in the 1870s and 1880s). If the lighter fabric over her legs is a skirt, rather than some kind of blanket, it appears that the bodice is cut straight across at the waist, rather than being pointed, and therefore might be from 1890 or later.

Taking all of this into account, the photo was most likely taken ca. 1899, possibly as late as 1901 or 1902 (taking the possibility of wearing clothing that was somewhat out-of-date into account).