YA 1990s. Set in 1920s. Girl visits flapper aunt.

A teen girl ( and possibly her younger brother) visit an aunt in the city for the summer. I think they were from the mountains and I think the city is Chattanooga. The aunt is a party girl. She has a boyfriend who drinks too much and maybe does drugs. The teen girl might be named Opal. That might be her mother’s name. Or there is opal jewelry. They ride the streetcar. I think the cover had a dark red border.