If you're on a meter, it doesn't matter what you're using your water for - watering the garden, using your toilets, filling your hot tub or even pouring it straight back down the drain - you pay more if you use more (already). Can't see the point of her comment and actually, tbf, don't see the problem with the number of toilets in the woman's home either: having six loos or twenty makes no difference as each person in the household can only use one toilet at a time. Mind you, if she was hosting a couple of football teams and feeding them Vindaloos, then that might put her usage up a bit, which (see above) she'd have to pay more for.
Can water companies impose a hosepipe ban, if we're paying via a meter for our water? This is not (I hope) similar to power cuts being enforced on us, as happened in the Seventies, unless water companies stop supplying individual premises. As you say, if you're on a meter, the use you make of the water is down to you, as you're paying for it.