I know I'm a stuck record on this, but one reason why Nick Ferrari is a great interviewer is that he is really good at 'just asking fairly gentle but serious questions that really show up where the interviewee is not across the detail'.
The thing is, this isn't some gotcha memory test about "what precise amount of money will this cost/raise" of the type beloved by interviewers in election campaigns.
It's the most basic question imaginable - "how will this thing work?" She has no idea.