Nora first came onto The Flash in the “Crisis on Earth-X” crossover, when she was a waitress at her parents’ wedding, before it got interrupted by crazy Nazis.
Cicada’s defeat resulted in Nora getting erased, but is it possible it was just a time remnant and not truly Nora?
Perhaps Nora was able to get back to the future before Cicada was defeated, and her time remnant was left behind.