She has such a lovely and sweet face. I might venture a guess at 1880s, perhaps the early to mid part of the decade. This is a bit difficult as she is sitting in such a way that we cannot get a very good look at her dress and the way it fits on the body, the lines of the skirt, etc. If I am seeing it correctly, her skirt appears to have an upsweep in the back with a ruffle pleated hem, and a bit of a bustle as well. Her dress is rather plain, although it was likely a good dress for her. So she may not be wearing the latest styles and it could be an older dress than the year the photo was taken. The sleeves and shoulders seem rather loose for the 1880s, almost as if the bodice is a bit too large for her. Again, that could be the way she is sitting.
This is just a guess, and I am sure some others will come along to give some advice.
Thank you for sharing her with us.