I guess the best way to explain turning back the clock is...[Give her a moment while she thinks about a good example to mention.]

Say you got into a fight and you got seriously hurt, potentially life-threatening. My hair can be used to heal the wounds that were given and potentially save that person from dying.

I guess another example I can use if my mother sometimes starts getting gray hairs and when I sing the song while she brushes she suddenly doesn't anymore.