Don't worry dear! EVERYONES hair is different. Stress to her how important it is to love herself just the way she is. As a parent, you can instill that in her, and she'll keep it with her forever.
I always say, "If your one of the few people in the world, lucky enough to be different, cherish that."
And, its so true!
Some kids hair just doesn't grow as fast as others. Her hair will grow in time.

