When I was a child with long, long hair, my mum used to wash it once a week and then I had to sit on a stool in front of while she brushed and combed it. All the time I just wanted to scream because it really hurt, but screaming would upset mum more so I had to hold it in.
DD hated it too. I hated it, because it made her scream. So one day I told her that I had to do it, and that she could scream if she wanted to, as loud as she wanted to and as much as she wanted to. She did. She also kept still and let me do it.
Before that,her screaming tensed me up and made it harder for both of us, but once she'd had permission to scream, it didn't upset me so much so I became less tense. This in turn made dd less tense and less sensitive to every little pull, and so she screamed less, so I was even less tense, so dd was less tense - see the pattern? 
I think it took less than a month for screams to stop altogether and she would sit quietly while I brushed her hair, nit-combed, parted plaited and styled.