I would say that when she asks, she's ready to discuss hair removal choices and care for the stuff that goes with it.
And shaving doesn't make it darker, though the colour can change due to hormones and other body changes. As someone who no longer shaves, I notice my hair gets darker in pregnancy and goes back to light soon afterwards so I guess the darkening common in teenagers that is attributed to shaving is likely due more due to their hormones than hair removal methods.