"That's what people do, even in the full face of the cameras, in such things."
You've unwittingly pointed to the crux of the matter. The whole point is that this isn't "in the full face of the cameras", it's a secret hearing process that other parts of the civilised world realised some time ago shouldn't be used. Read the article and you'll find that that's exactly what she's objecting to.
Testifying in open court is something else entirely. The defendant is aware of the process and can challenge the evidence. The Grand Jury is a secretive, one-sided process with all the coercive powers of a court and none of the safeguards.