What a great find! August Schuffert (1866-1936) was a German-born photographer who gained his photographic education in Germany and then settled in Turku in 1885. Schuffert moved frequently, and he ran several (4-5) studios around Finland. Schuffert owned a studio in Tampere at Hämeentie, nr 29, from 1901 until 1923, and in Turku at Eerikinkatu, nr 15, from 1899 until 1920. Both studios are mentioned on the reverse side of your "carte de visite", which leads me to the conclusion that the photo was taken after 1901. You mentioned that your great-grandmother immigrated to America around 1910. In my opinion the woman in the photo could easily be 18 years old, or in her early twenties.
 
Schuffert's studios were so many that he couldn't work as the main photographer in all of them. In effect, he had several assistants and professional photographers, mainly women, taking care of the studios' daily photographing practices. One of them was Martta Terävä, who worked in the Tampere studio, and she might have been the one who photographed your great-grandmother. As a curiosity, I'll attach here a photo from our museum's collection which has been taken in Schuffert's studio in Turku, around 1900-1910. You may recognize an identical backcloth with the birch motif as is in your photo. It was quite common to have studio equipment serving for several years and then moving or selling it to another studio.

You'll find more information on August Shuffert and Martta Terävä and other Finnish photographers (in Finnish) on our online service, Kuka kuvasi.
All the best and good luck with your research!