A wise man said 'This is the art of wei wu wei: to act without action.'
__________________________________________________________________
My first reaction would be to ask, what, if any, scientific evidence does she have for saying this occurs in humans? But better to leave sleeping wild animals be.

She seems to be confusing the concept of hormesis with environmentally sourced pathology. This is most illogical.
Does she have any science to back up her arguments? But better to leave good enough alone.

If your daughter consumes less of the mass produced dairy products than her peers do, this would not surprise me. Mass-produced dairy usually has relatively large amounts of bovine growth hormone in it. Hint: It's action doesn't magically stop at the bovine teet.

A student of history she is not. There are too many examples to list, but the Warsaw Ghetto history lesson wouldn't be a poor choice for someone's starting point. But better to leave good enough alone.

My condolences to you.

I can think of worse problems than that. Why not just accept it and move on? You can always try to use your own lifestyle choices and actions to become a good example for others. That way, no words are necessary.

In the grand scheme of things, on what basis have you decided that she, or you, or anyone, would somehow be in dire need of convincing?

Don't mention it R.W. Best wishes on creating a stress-free environment for your family.

This could be actually possible if she is extremely non sick. Little kids should be sick, but should have mild symptoms, that don't require doctor visits and that only mildly influence course of the babies day.
Since you say she is sick less often, then I think C works as it should. I see exactly the same phenomena with my daughter - 1 to 2 days of mild sickness every month or so. And one that lasts for 7 days every 3 months or so. I give her 2x1g of vitamin C in normal condition and higher when sick along with cod liver oil, fish oil, vitamin D, zinc, kelp, Mg, Ehinacea,multivitamin etc...
My experience is extremely positive at this moment and let me just say that she attends kindergarten where half of the kids are sick every day.

But how to fix your problem ? Solution is easy really - she doesn't have to know !
You can put powder in her food or juice when she doesn't watch.

You can't fight unreasonable attitude with reason. There might be some few reasonable objections against vitamin C megadoses for kids but she expressed none of those (for instance it might promote esophageal pain or gastric pain theoretically, or even metabolic conditioning, but I still think that even if it happens its nothing compared to benefits). As for her other objections, those are, well, fantasies, and you know you can't reason with woman.

Daughter took 1 gm/day C from weaning, then 1gm/day/year of age after up to 10. More if any sign of any problem.
Her question - "what is sick?"
Ans: "sick is what happens when you go to college and don't take your vitamins."
Only took one time to fix that error.

FRM