But see, it's actually exactly the reason why what they are saying is so wrong. They think chemicals are only things that come from laboratory beakers, but the foods we find in nature are ultimately made of the same chemicals, and whether a certain chemical is "natural" or "artificial" is not what determines its toxicity. Some "natural" chemicals are toxic, and some "artificial" ones are not. And scary-sounding chemical nomenclature is not a basis for figuring out which ones are harmful (and in what doses) and which ones are not. In small enough doses, most things seem to be OK, while even things we tend to think of as safe and natural can have harmful effects if the dose is too high.
Her framework is just plain wrong, even giving her the most generous reading. For virtually all chemicals (maybe all?), both artificial and naturally occurring ones, there is an acceptable dose which does not cause any discernible (or demonstrable) harm. If she wants to say that a certain chemical does cause harm in any dose, she needs to demonstrate that. And just because a chemical may cause harm in very high doses, does not mean that low doses are harmful. Salt (sodium chloride) is one simple example: too much of it is bad for you, but so is not enough of it. Same with water.