When the women I know speak of getting or having their hair 'done', it's a multi-step process which, depending on her style preference, may involve washing, cutting, styling, perming, curling, dyeing, drying, weaves, extensions, and other processes I'm not even aware of.
It's much more involved than one single action, as opposed to just cutting or combing.
My experiences have been that even when just getting ready to leave the house, a woman 'doing' her hair seems to be a mysteriously long process involving many steps.
I've learned that "I'll be ready in a moment, I just need to do my hair" actually means I've got time to read at least one or two more chapters in whatever book I'm currently reading.