I think you are missing the big picture.
The prosecutor is establishing privileged information and dates around when information has been made available.
Why?
Because she is going to later provide additional details, including who drove her home, based on information that was received outside of the dates where info was public domain.
Yes, Mitchell is speaking on behalf of the Republicans and their investigators. Grassley failed to mention that they have investigators and have been investigating. She is asking necessary questions, others will draw the conclusions as that is not her role.