However, you would be wise not to try to lift too much after a heavy shower has passed through!
Of course humidity is only going to affect you if your first limit is the engine output - correct? i.e. Temp or Gas Generator speed.
To be realistic 0-100% makes a difference of 400' as Nick L sez........working backwards via my RFM on the current type, when NOT limited by engine output, that makes a difference of about 20 kg to 25 kg or ~ 50 to 60 lbs (.8% of MTOW)
If this is stopping you from getting airborne I would be worried! In other words if I pulled T/O power and waited about 5 mins the effect would be negated.
Easy fix - stop listening to the wife or better still, throw her out!