I would estimate 1901-1919, considering the hair style, the rimmed eyeglasses, and clothing. You'll notice the upswept hair style is decidedly Gibson Girl era (1890-1918). Following World War I, the Gibson Girl look waned in popularity to be replaced by the less ornate style of the 1920s. She clutches a pair of gloves which also fell out of fashion by the 1920s. Her sleeve "poufs" are not as exaggerated as the the 1890s, nor does she appear to be wearing a bustle. Her plain, severe collar suggests turn of the century to about 1910-ish. The flower-adorned hat (even without the usual scarf/veil) looks to be an early automobile-suited affair, again suggesting early 1900s.
I looked at my books and the hat style went out by about 1905. I found a dress and a hat much like she was wearing dated 1901. However the fashion was very similar from about 1897-1905. So I would date it during this time period.