The Supergirl of 1959-1986 had a rich history in the comics that was wiped away after John Byrne's The Man of Steel hit the stands. Infinite Crisis could have been the perfect opportunity to make this iteration of the character canon again, but a few years prior Kara Zor El was rebooted in the pages of Superman/Batman, making it impossible for the Silver Age Supergirl to ever have existed in Post Crisis continuity.