If "Brer" means "Brother", what is used for females in Folklore?

As a New Englander, born and bread, I'm not up on the dialect of that part of the country. I know Bre'er Rabit and Bre'er Fox came to us from Africa from the Gullah culture of South Carolina and Georgia, I've always assumed that Bre'er was a Gullah word. I don't know the word for Sister, but that would be your Mouse's honorific -- Sister Mouse. If you aren't down with the dialect, skip it. Just call her Sister Mouse and write it as well as you can, with no affectation.