We don't know the name of the woman in this 1860s tintype, but we do know that the image was created at Brownell's Gallery in Sparta, Wisconsin. I haven't been able to find much on this gallery online, which leads me to believe it may not have been in business very long. I did find a 22-year-old Muth/Matt(?) Brownell, photographer, in the 1870 Census living in Sparta. He was born in Vermont. He doesn't appear in the later censuses in Sparta.
It's also a shame that the mottled image doesn't allow us a clearer look at the subject of the photo.