I think the choice of World War I is to give her a strong motive for dumping humanity for X number of years, since it had an arguably greater psychic impact than WW II, having been the first modern war of its scale. Not that WW II wasn't horrible enough, but WW I was "The War to End All Wars," because of the public's newfound awareness of the horrors of war. It's also a lot murkier in its motivations, without as clear of a division of good and evil, and would appear to an outsider in a much more negative light than stopping the Axis would. There was a bit of discussion over that choice in the WW movie thread. I think it's a choice that could work pretty well.
I like the choice of having her outfox Bats. I'm guessing it was more intended to show her as having been around the block a few times/the wisdom that comes with her age vs. his high intellect, than to turn her into a Black Widow type. (Though that's a perfectly plausible theory, too, the way Hollywood execs think -- "like that but different" being a rallying cry for most of them.)