Have her lawyers not been sharing all relevant information with her–Grassley's letter to attys. offered to do hearing in CA, she seemed to be unaware of that. Lawyers probably wanted it in DC because it could be a bigger spectacle.
No need for Mitchell to talk about polygraph protocol at the hearing. She can explain it to Rep senators when she does a debrief. They are all attorneys and many probably already know about polygraphs. With eleven 5 minute intervals she has a clear set of priorities and a plan for order of her questions.
Personal opinion, behind that everybody's-favorite-aunt persona, she is a lethal prosecutor. Reputation is she is fair, so she will be incisive with BK also.