I'd prefer they make the 1940s Black Canary an aunt of present-day Dinah's rather than a grandmother or great-grandmother. More flexibility when it comes to aging there since an "aunt" could easily be a great aunt or great, great aunt but still be referred to as just an "aunt".
When I was growing up I had an Aunt Loretta who was actually my father's aunt / my grandmother's sister, but we kids just referred to her as "aunt".