She wasn't.
That story (in All-Star Squadron Annual #3) was set around the time of All Star Comics #8 (December 1941-January 1942).
In the All-Star Squadron Annual's story, Roy also included reasons why Hourman and Green Lantern gave up their membership slots for Starman and Dr. Mid-Nite.
Black Canary's first appearance in a Justice Society of America story was in All-Star Comics #38 (December 1947-January 1948).