As you said, that is ridiculous. So much so, that I don't think I'd even be bothered to respond to her. If the next time you request wipes and she says something about how quickly you're going through them, then address the issue than.

I have a similar situation with two of my young ones...they poop frequently through the day and they are not "clean" poopers...sounds funny...but what I mean is I have one that poops out a nice ball of poop. The other two always have very soft poop that is in every knook and cranny...and takes lots of wipes to clean up.

I'll use anywhere from 1 - 3 wipes for poo and on the occassion I've even used 4.

If the parent ever said anything, explain that the child poops more than once and you are careful with the wipes but with that said, you'll use what you feel is necessary to clean the child and to keep your hands free and clear of poop.