We would have healed Babylon. Experience shows that it is useless to attempt to correct such inveterate evils. Everyone into his own country (as Jeremiah 50:16). Her judgment; i.e. her punishment. Perhaps there is an allusion to the fate of Sodom and Gomorrah, burned by fire from heaven.
But we might also render "her crime" (comp. Deuteronomy 19:6, where "worthy of death" is more strictly "a capital crime").