She should smuggle a little whiteboard and a dry erase marker onto the stage. And strike a line on the whiteboard each time he lies. If Trump can use a marker during an official presidential event to clumsily (and incompetently) predict where a hurricane will hit, she should be able to use in during a debate.
Sure the board would be full within a few minutes. But at least this way she'd have a better way of showing the volume of lies he spews.
Plus it would drive him fucking insane, which would be hilarious to watch.