Likeliest explanation that occurs to me is that some federal agency told her that hushing the matter up was a matter of national security. Would explain the judge going along.
Those requests do not go to some lowly ADA, nor is an ADA authorized to make the decision. If she'd been approached by the feds, she would have to inform her boss. The feds go to the top guy, the District Attorney. The DA makes the decision whether to go along with it, then tells the ADA and the feds what he's going to do. In other words, it doesn't come from the bottom up, but the top down.