In addition to the server, Hilary "abandoned secure line to use home phone"

[Wyrd of Gawd]

If you want to label it as lacking common sense, then sure. However I would go slightly further than that. When you are given security clearance and are going to handle sensitive information, you usually have to read and sign a document stating that you understand the procedures in place, and the importance of handling sensitive data properly. So at the very least, she knew what the procedures were (assuming she actually read the document) and skirted around some of them.

Having held a Secret clearance myself, I can attest that yes, you must sign documents (multiple, not just one) attesting to your understanding  of sensitive handling.

I do think that ex post facto classification is an odd circumstance and may afford her wiggle-room.

To my mind that still bespeaks a lack of common-sense; however data might be classified by the government, it should be apparent to someone especially in such a high position (assuming they have knowledge on the topic at hand) that sensitive data is, well, sensitive.

To put it terms of my experience: the number of bombers at my base during Desert Storm was not classified, but it wasn't information I talked about, period. It seemed to me that discretion wasn't just the better part of valor, but also security. We got that sort of indoctrination in Basic Training, that even a portion of the truth can help an active intel  operation.

Disqualifier? I'm not so sure. Evidence of sloppy thinking? No doubt.

You nailed another one.