Rick:
I'm wondering if the woman in the tintype is really your great-grandmother - if perhaps it's another relative.
The reason is her dress, which is more from the 1860s, before your great-grandmother was born. Women's fashion changed dramatically in the years after the Civil War, going from the hoop-skirted look seen here, to narrow skirts with a bustle in the back. The movie version of Gone With the Wind shows the change very well - Scarlett loves her hoopskirts until the war, and then afterwards, begins dressing in the new fashions.
The hairstyle seen in the photo is also pre-war; it's called a chignon, meaning that the hair was pulled back and gathered into a large bun at the nape of the neck. After the war, hair was worn more on top of the head. The woman's lace mitts (the fingerless, decorative gloves) are another pre-war touch.
Women everywhere in America were as fashion-conscious as they could possibly afford to be back then. There was Godey's Ladies' Book and the Woman's Home Companion to show them the latest styles from Paris, and the new widespread availability of the Singer sewing machine made it possible for them to make what they saw.
There are, of course, other explanations for the fashion in the photo - it could be a case of a young woman dressing up for a costume party in something of her mother's, or similar (people were very social back then; there were not many amusements nor much entertainment, so social events were what they did for leisure). But the dress is way more 1860's than 1890's, when your great-grandmother would have been a young woman. And by the 1890's, a tintype is not likely.
So, it makes me wonder. Whoever she is, she's beautiful. And she has your eyes.
[this post was last edited: 1/24/2013-06:51]