She's just so clearly uncomfortable in these situations, and I think people know it. I don't see hundreds of posts saying how awesome she was; I don't see us showered with threads where people are repeating favorite bits, as they were when the lovefest was first starting.
I like everything about her, but man, she's dying in these interviews. Like it or not, in what could be a razor-sharp race (or not), this could be fatal.
On that specific response, I agree. However, I think the truth is that the accusation had just come out, and she probably didn’t know enough at that time to give a better answer. IIRC, the accusation was first made hours before the interview. I suspect McCain’s staff was still digging in to the details, and it would have been far worse if she had offered INCORRECT details as part of her answer.