As a fashion historian I would agree with a date of date the last quarter of the 19th century, but you could hone in on a closer date by looking at books like Joan Severa's,
Dressed for the Photographer: Ordinary Americans & Fashion, 1840-1900. I would focus on the pin on her shoulder as I wonder if it is a membership pin that was significant for your community. I don't know how much you can make out about that area of the photo. In the larger image is there decoration on the shoulder or is the sleeve smooth at the top? I thought there was some decoration on her right shoulder, but that might be from the person taking the picture. I agree that talking with churches and other leaders in the black community would be helpful.
------------------------------
Marian Ann Montgomery PhD
Curator of Clothing and Textiles
Museum of Texas Tech University
Lubbock TX
------------------------------