This is actually excellent advice. Positive reinforcement is one of the things I have tried whenever she has brought up her worry (usually at bedtime after an episode of seeing blood during the day). She is bright, so she understands that blood is a good thing for our bodies and that it carries oxygen and other things to help keep the body healthy and working. It's like she absolutely understands that there is no reason to react to blood, she has even asked why her body does this (vomiting/fainting) when no one else's does? I wonder if there is a book on the body that I could use to help... I'll start googling now.
It was suggested that we try playing with fake blood, that you get for Halloween face painting? But again I don't want to start 'treating her' myself as I have no clue what will make it better or worse??