I don't mind her flaunting, I do mind artists and authors flaunting her *at* us.
Precisely. That's why I don't see why the window requires any explanation at all. Plenty of buxom women wear low necklines without expecting - let alone wanting! - to be leered at. It's the men that are the problem, not the choice of clothes. The comic book equivalent to that is that it's the way artists draw PG that is problematic, not the design of her costume per se.
Trying to 'explain' the costume just draws unwarranted attention to what isn't, in fact, the problem. And covering up her cleavage would, I'd argue, be conceding the sexist point, just as women shouldn't have to cover up just because some arseholes won't look them in the eye.