I need to act indifferent when she comes home without appearing to be instituting some sort of Plan.
Will it be that obvious if all of a sudden I start to 180 her?
From my perspective, Oxford, "indifferent" is pretty much how you have treated her in-your-face affair from the get-go, so NO -- I don't think she'll see that as a "180" at all, no worries.
Finding all of her stuff, boxed up and out on the lawn when she got home? Now THAT would be perceived as a "180!"