"Nailed" is a strange word. You seem to suggest the FAA has people sitting around watching video from under bridges, just in case someone flies under one. "Nailed" surely doesn't mean 3 shifts of people employed to watch bridge video footage. Surely it means, "I think she flew under that bridge. Get the footage for XYZ period of time and see if she did." In this case, there would be a reason to think she flew under the bridge at a specific time, rather than 3 shifts of folks for every bridge, watching video in case someone breaks the rules. . . not that that also wouldn't be troubling. I also kind of ask myself about the conversation that had to have taken place between the DOT and the FAA, because surely the camera belongs to the DOT. How does the FAA even know there's a bridge there with a camera on it?
And, yes, the FAA's accusation is that she turned her transponder off before going under the bridge, which is what they yanked the license for. She disputes that. However, what led to to that? Was it blurry eyed folks finally seeing a plane fly under a bridge, or was it a gap in ADS-B data? It was suggested that squawking 1200 makes one anonymous, and yet the yanked her license because they contend she shutoff her ADS-B out equiped transponder, while she was obviously not under any sort of flight following (so, squawking 1200). There could be an argument that anonymous ADS-B data led to the examination of the bridge. It could be a good argument for anonymity, and a BAD argument for the FAA, because that would mean they have algorithms examining ADS-B data, looking for any "no harm" event so they can yank licenses, and then looking for a way to de-anonymize the trace. I mean, it's a good argument, but doesn't make the FAA any less gestapo-like.
I would also like to point out that your ADS-B equipment need not know your N number for the FAA to de-anonymize your ADS-B trace. I'm a career software engineer, having been in the business for more than 3 decades. I mention it because this problem is a "rendezvous" or an "appointment" in the trade. My understanding is that your ADS-B device transmits a unique identifer for the device, something like a MAC ID used in a network card. As a result, whenever you fly into controlled space and the blip on the screen is married to your N number, it IS married. All they have to do is record that the "MAC ID" received = your N number. . . Until a new N number is associated with that ADS-B id. All it takes is one flight into a Class C, and you could be forever not anonymous even while squawking 1200. I'm not saying the FAA does this, just that it can be done, and, really, is the intent of ADS-B; wihci is to replace radar. That marriage in a radar world was obviously only temporary, your N-number was married to a squawk code. In an ADS-B world, to make it temporary you'd have to choose to remove the "marriage", rather leave it there and just change the squawk code associated with it. The data was distributed in a radar world, with you being handed off (inserted into a new system, and removed from the previous -- to preserve squawk codes) if under flight following. With ADS-B, its one system. The squawk code is the "rendezvous", the N-number of MAC ID need not be.