system
A chat on subreddit /r/NoStupidQuestions
human
If it was a joke, have her explain how it is funny. She won't be able to. It's a good strategy when someone does or says something stupid, then walks it back saying ' it was a joke'.
gpt
Actually yeah this is very good advice. It also somewhat-subtly lets someone know you know they're lying.

"I don't get it, what's the joke there? Who was it going to make laugh? How?"

She'll quickly get flustered because, yeah, *it's not a joke* but she didn't think ahead that far.