I am not going to let DD eat carbs [...] and then say, see what happens when you don't eat your fruit and vegetables. What kind of advice is that?
In our house, we call that an "object lesson." Or in today's political parlance, a "teachable moment."
You can tell a kid a thousand times, "Don't touch the stove -- it's hot." But they will never, EVER get it until they touch the danged stove. I let our son touch the stove when he was little, and although it didn't melt off any skin, he sure as heck doesn't touch the stove any more.
If she had diabetes and chose to eat sugar would you wait until she was in convulsions and say, see what happens when you eat candy?
C'mon, now. I wouldn't let our kid eat PB either, if it would send him into anaphyl-whatever shock. That's just plain nuts and I don't think it's reasonably analogous.
And how many of parents out there have to "force" kids to do homework.
"Forced" to do it at the point of a rubber-band-gun, no less. Only because the object lesson involved can take a little while to materialize. I do, however, let sloppy work get through so he can get the immediate teacher feedback in the form of an "F" for turning in illegible work, despite having all correct answers. He only got one of those and is much more mindful of his "neatness" and when I do have to "suggest" that he rewrite something for clarity, he doesn't pitch a fit like he used to.
I'm not one for wrapping everything in cotton balls. My wife & I went round & round about the blasted pads on all the sharp corners, or always trying to prevent the myriad of cuts & scrapes. Grrrr.
If the object lesson will be readily apparent and not threatening to life, limb or eyeball -- nothing teaches like experience.