The real-life song was first really sung for the movie. And the movie has been reinterpreted as an in-world movie.
But what song(s) did Minmay actually sing during the great battle against Bodolza? Did she only sing her familiar TV series songs, as in Ep.27? Or did she, perhaps, sing "DYRL?"?
I don't like the idea that such a classic song only originated years, or even decades, after the Space War, during the filming of the in-world movie, with Minmay & Co. detached somewhere way out there in deep space. I like to think of it as actually being deeply connected with the important events of the series.
But I can understand if a serious review of the facts points in a different direction.