Black Canary was indeed a member of the JSA and joined much earlier than 1947 in the planned DC Timeline that Didio leaked. Who knows if that's still in play, but I don't see why not. Retroactively having Black Canary joining the JSA and JLA works better for and new stories set in the past. The more female superheroines we can get in flashback tales, the better. And, in the original stories in which Black Canary doesn't appear, she was off on another case that day