OK, you've a habit. That fills a need but you'd like to stop it.
a) stop the habit (but wait, easy to say but that's almost impossible in practice)
b) my suggestion: think of a substitute habit that satisfies the need that the humming satisfies [it's much easier to swap habits than it is to drop one)
Such as:
- (probably won't work without diligent practice and even then it might not be manageable) humming to yourself just in your mind (same thing as reading to yourself without saying the words)
- carry a pocket timer, try to Not hum for X minutes, get used to that and then steadily over weeks, months, extend the amount of time on the timer (this will: train you to develop conscious control over your humming, and, build your tolerance for being hum free)
- try substitute activities, such as finger tapping or rubbing, or snapping a rubber band on your wrist, against your wrist (perhaps for set timed periods at first as you get used to it being a substitute for humming)
Oh, or:
(c) buy your daughter some earplugs. I doubt if strangers would be offended (though they might think humming loudly was odd), but undoubtedly your daughter's become sensitized and may deserve a break from mom's humming especially while out shopping
Lovely. You are musical and happy! Good for you! I hum a lot too and it drives my poor wife mad. But what the hell? Must we always be labeling normal behavior and medicalizing things? Hum away I say. Lets hear it for the hummers!