Cuddy has had many years to ponder the past and wonder where things went wrong. I don't know whether what she remembers of the past is in any way an accurate picture of what actually happened (selective memory and selective perception), but the distance between then and now probably helps her to analyse the group dynamic between her, House and Wilson more accurately.

And the momentary situation is pretty clear-cut: Wilson has no contact with House, Cuddy has. He wants her to give up her contact on the off-chance of that actually helping to keep House in the dark. One doesn't have to be a psychologist to realise that Wilson is being a bit of a dog-in-the-manger here.

I considered different options for the revelation, but this one was nicely dramatic, in the place that is the epicentre of the series (not some other random location), and it hits House/Pete totally unprepared - he isn't even on his quest at the moment, he's 'off work', so to say.