Lorraine 46, tampons probably are necessary for girls involved in things like competitive swimming, dance, gymnastics and similar sports involving close-fitting lycra and/or water. If you're at a competitive level, you can't just not train when you've got your period
I would always prefer cups.
As things are, I only use pads myself, because I just know I would forget to remove a cup or tampon, but since cups are much less risky, I would always prefer them to tampons.
Also, some tampons are more risky than others. I'd stick to those made of natural materials.
(I was very shocked to learn that there is no medical testing required for tampons. WTF?)
As for the initial post ... it is rather easy, if the girl wanted a demonstration, then it's okay, if she didn't want, then it is not. (I am not comfortable with the level of nudity my parents are comfortable with, so that is possible.)