She is from a parallel Earth, after all. And the only actual mention of "the Second World War" in the movie is in the very first line of the opening narration. If her world had multiple 20th-century wars, as she said, and none of them was named "the Second World War" or WWII (the War of the Americas seems to be the closest equivalent), then she might not have understood which war was being referred to. The movie assumes, of course, that the audience knows the basics of the real-world geopolitical situation it's based on. So someone from another Earth with another history would miss a lot of the references. Okay, so it's the early 1940s, and Germany has occupied France and other parts of Europe, and they have a presence in North Africa, and America is in some sort of adversarial role to them, and...?
Indeed, the whole subtext of the movie depends on the viewer already being aware of WWII. After all, it was meant as a pro-intervention allegory. Rick represented the United States and its resistance to getting involved in the war, and his journey to the realization that he had to get involved, to sacrifice his self-interest and fight for the good of others, was a statement about how America needed to do the same. Someone who doesn't even know what World War II was would have a hard time getting the nuances.
Weren't you just saying you wanted the characters to be more 3-dimensional? Besides, it's Casablanca, arguably the most perfect film ever made. And it's a Warner Bros. film, unlike any of the ones you named (although WB distributed the second one).
Consider this: maybe the choice was deliberate foreshadowing. After all, the scene they were showing was about two lovers who came from different worlds and had tried to come together, but were now realizing that they had to stay apart for the greater good. That might well be a hint about where the Wally-Jesse relationship is going.
A lot of people believe Heaven is a good place, yet they still don't want their loved ones to die. The Speed Force is basically Speedster Heaven. If Wally is trapped there forever, then he's effectively dead.
