A girl who is about 7 or 8 was playing in the park with my kids the other day - I was bf'ing my 9 mo and the girl started playing with her toes. I said, 'she's nursing right now, and will be ready to play in a few minutes'. Girl says, 'she's doing what?' (sincere unknowing, not disgust). So I say, 'she's breastfeeding, drinking milk from my breast. Girl "really?"

"but, how does she do that?"
The mom wasn't around, so I said when a woman has a baby, her breasts automatically make milk for the baby to drink, and the baby just knows how to drink it, because that is what babies are supposed to drink.
Yeah, if the mom was there, I might have not said as much. I think that just what you said is enough to put the idea in her head. The next time she sees someone else bf'ing, or sees you, she'll remember, and gradually it may seem more normal. By the time she has her own babies, maybe she'll have seen hundreds of positive nursing images (we can hope) and she'll have a more balanced view.