I'm a big fan of hers and I love how she's used her big brain and legal expertise in these hearings. With that being said, my impression is that she asked him a "gotcha" type of question she doesn't know the answer to. She should know the answer before pushing him on this. She also put words in his mouth, "are you certain you have not..." and he hadn't made a statement of denial and had to correct her.
I wonder if any of it even matters. They sure seem powerless to stop the appointment. IMO, she went for a kill shot and missed. That's worse than not going for it in the first place. We'll see what happens but we're probably fucked. Kavanaugh gets in and it'll be much easier from trump to challenge Mueller, his findings and any questions about an interview which he refuses to do since Kavanaugh's down with that.