It's not the traditional intolerance you are thinking of. It causes severe behavioral issues with her, usually involving depression and severe anger. We've been feeding our baby raw milk since she was six months old, so we had plenty around for my eldest to try. Raw milk, real yogurt, homemade cheese, plus everything processed has the same effect on her. It is nearly impossible to keep a nine year old away from dairy, so a great many days are challenging. And there are no ways to medicate for it, especially since we'd never allow it. The severity is dependant entirely on her consumption. So where she might need a double dose of anti-depressants one day, it would be considered an overdose a week later.
Sometimes I wonder if an autistic child would be easier. You can know and understand they have an uncontrollable problem. With this, she knows it's bad for her and the effects it has, but she sneaks it anyway. It's a personal choice, and although she is almost nine, you can't blame her for wanting what everyone else has. But you have to hold her responsible for her behavior, too.