I have CIE and when I was younger my face was always red. Now it just has a slight pink glow (I'm 32).
The days that my face is red on it's own (without being hot or exercising) is because I am dehydrated and dry. I make sure I drink a lot of water, which does wonders for my body no matter what any doctor says. Usually when I put lotion on my face, it does get a bit red, but then goes back to pink. I think this is a thing that improves with age.
As for things to say. She'll learn what makes her comfortable to say as she gets older. When I was young, my parents told me to just say that I had a skin condition. For some reason that seemed to work. I guess people didn't know what to say after that. As for now,if someone is being rude, just look at them and say I would love to have that healthy glow that my daughter has. Can you imagine all the money she's going to save on makeup?