Sit down and talk to her and tell her she needs to stop gaslighting you. If she can't be honest then that's a huge issue.

You've *LITERALLY* caught her in the act.

The only extra step you could do is install a hidden camera and that's... problematic on it's own. But that would be "look. you can't deny this." to a new level - but that would be over the line to be honest for something you ALREADY know to be true.

I don't know if I'd say end the relationship but counseling or something to bring out that yes, she is in fact doing this and it's affecting your relationship to be lying about it.