It's truely amazing how the DC Universe works... or doesn't work as the case may be? For instance, in Midway City there were two teams of heroes, Hawkman and Hawkgirl as well as the Doom Patrol, and yet they never met despite operating there around the same period of time! Then there are the Batmen of two worlds who never met even though their Justice League and Society mates teamed up repeatedly throughout the decades. And then, there is what could have been, the courtship of Supergirl and Firestorm! Why would we ponder this concept?
Consider how, each years during a few crossovers between the League and Society, Firestorm of Earth-One and Power Girl of Earth-Two worked together on various cases and grew fond of each other. Alas, living in two separate universes would cause a strain on any budding relationship. However, had the Nuclear Man only considered that the object of his effection had a counterpart on his own planet, Kara Zor-El instead of Zor-L. Sure she had on-again off-again relationships as had he, yet had they have met no doubt sparks would've flown. Who knows?