Kelly I've read that your nipples absorb the babies saliva and that tells your body to make exactly what the baby needs. So if they're dehydrated, it'll make more of the watery foremilk.
If she comes up with ideas like that that you don't like, sort of laugh them off and say "did people really do that? That's an old fashioned idea these days". Hopefully that will get her to back off without you having to get too forceful and say "my baby, my rules!"