We’ve seen a number of suggestions about how she should respond if he brings that up. My answer is that she should ignore it if he brings it up or if the mods ask her about it (at least as a followup to his ramblings), similar to your response, that she should essentially brush it off and get back to the actual question.
However, I think if, as soon as Trump brings it up, the other camera catches Harris mid eye roll, it’ll make for a great meme. We got a lot of mileage out of Fauci’s facepalm and I think we could get even more from a well timed, memable Harris eye roll.