So my weird fanfic idea about that would be that after "Prisoners of 3 Worlds" Batman took the crew to Superman's Fortress of Solitude - Supes would verify and help cure any 'alien' traces to the gases they were exposed to in the classic Silver Age story. Kal told Robin and Bat-girl the legend of Nightwing and Flamebird at this time - they were in the Fortress, probably saw the city of Kandor, etc, etc.
But maybe part of the cure involved some Krytonian 'cocktail'... and later she received some minor power ups.