Is this like how the 7-11s in my city blare opera music to keep tweakers from hanging around outside?

You definitely need to have a sit down talk about how the lies are affecting your mental health and tbh probably your ability to trust her also. Its weird she is lying about it. Maybe she is embarrassed which would make some sense as most women are not as open about masturbating as men are but at the point that it is making you feel insane that embarrassment is not worth hiding this over.