Justice League of America #220

"The Doppelgänger Gambit"

Earth-One's Johnny Thunder reveals the origin behind the second Canary, placed in limbo by Earth-Two's Johnny Thunder at the Earth-One Superman's request following their battle vs. Aquarius, since Aquarius's radiation was killing her as she crossed to Earth-One after her husband's death. She was then replaced by her daughter, whose memory had been replaced with her's. The heroes defeat the Earth-One Thunder alongside the Earth-Two counterpart, while the revived JLA aid their JSA allies on Earth-One. The current Canary has her original memory restored and leaves with Superman back to Earth-One.