Yeah I guess that would work. Oh gosh, I can just imagine the fan reactions if Black Widow was indeed the Skrull Queen the whole time since The Avengers for example, meaning that she could have been switched out after Iron Man 2 but before The Avengers or something. It would be a pretty polarizing twist, on one hand it would've cleverly converted the team formation into some ploy done by the Skrulls so Earth doesn't belong to Loki and Thanos so that their Skrull agents could continue taking it. Some would see it as clever and shocking, but on the other hand we really did only get attached to Black Widow with The Avengers and Cap 2, so it would be a heart-breaking blow thus making the Mandarin Twist look like nothing. People would never watch The Avengers the same way again.