What are you doing now?
We might have better suggs if we know what doesn't work. Also, what's wrong with her hair now?
If it's dry/frizzy, have you tried skipping shampoo and washing with conditioner only? Suave coconut works well for my DD. The conditioner has enough surfectants in to get the hair clean. Also, if you're not leaving conditioner in, that might make a huge difference. Leave it in so that it's so thick you can see it--it disappears when it dries. I got this advice years ago from someone with 3c hair and it's been a lifesaver for us.