I am assuming your daughter is blonde. Wash her hair, towel dry, and then smother it in tomato ketchup and leave for half an hour. When it washes out the red should have neutralised the green (opposite colours)
Lets try something a bit less odorous? Look for shampoos that are labelled anti-chlorine. Anything containing sodium thiosulphate should do nicely. The green colour comes from the chlorine in the water. The thiosulphate will counteract it.
Just a ps. to my question: I have heard of ketchup before, so I did give it a go, and how amazing! It really worked!! She does smell a little like a fast food restaurant though! Thanx all.
5029's answer is interesting. I carn't believe that the result is due to colour mixing.... is it perhaps the vinager in the sauce? Anyone know what causes the colour change? ( I will understand detailed chemistry)
Hamish