Well, I hadn't read STARS AND S.T.R.I.P.E., but did she get the braces back in that run, or during JSA (which I have read, but can't recall anything about the braces)? It might have been established back then, which Johns would have written. If not, yeah, it comes out of left field.
Let me put my reaction to you this way: this is the first JUSTICE SOCIETY issue to actually get a rise out of me at all, as opposed to all the stuff you mention which just left be cold, so much so that I barely pay attention to it.
Thus for me, it's not making a leap at all, but rather a, "Oh, finally, here's an issue where something silly and fun is happening! Fuck it, I'll take it!" Does that make sense?