S.H.
I have a daughter like that.
The way I solved it is:
1) Got a detangling hair brush. THIS one:
http://www.sephora.com/browse/product.jhtml?id=P241318&am... It is WORTH the price, believe me.
It does work.... and even if there are tangles... the brush makes it easier to get it out... without all that harsh pulling/tugging at the child's head.
2) Got her satin pillow case. It prevents tangles
3) Use a leave-in hair cream/conditioner. I like the brand "Garnier Fructis." Works real well. Or the brand TIGI "After Party." These are BOTH GREAT GREAT hair products.... for conditioning AND getting tangles out and preventing it. I used it too.
THIS, has really improved her hair, lessened tangles, AND lessened her screaming as I brush her hair. IN fact, she can NOW brush her hair herself... AND the tangles too, which is now less.
AND I always trim her hair regularly, to get rid of split-ends... which also contributes to tangles.
ALSO, brush her hair before bed, and she puts her hair in a low pony tail, before bed.
My daughter's hair is a below the shoulder length.
all the best,
Susan