What year did Supergirl get published by DC Comics?

According to Google, it was 1959. 🙄

arohanui, According to a number of sources, (in a film, television series, or other fictional work) a piece of new information that imposes a different interpretation on previously described events, typically used to facilitate a dramatic plot shift or account for an inconsistency.

I remember her from before the 70s. And what is retconning????