First of all try to make her morally strong and confident by saying lifestories of great people who were dark complexioned. Even now there are many. You may tell them about Indian diety 'Krishna goo who was called Kaliya.
However pl do not fall prey to chemical creams. It will ruin tender skin if the child.
1. Use raw milk with a swab to clean the skin in circular motions. Let dry. Wash with
cold water.
2. Use Honey, rose extract, Kesar 2-3 stigma powdered, a pinch if pure turmeric and fine gram flour to make fine paste by adding little raw milk. Apply layer on the face. Let dry or keep for twenty minutes whichever later. Wash with cold water.
3. Once a week use common salt and honey as exfoliating paste and rinse after sometime with cold water.
Orally start giving her Sitopaladi 100 gm + Prawal Pishti 5 gm and mix well and give 1tsp in honey twice a day. Give continuously.
Liquid Mahamanjishthadi Kvath 10 ml + water twice daily.
All medicines are Ayurvedic, no side effects. Commonly available in India. Elsewhere please find on net.
Hope it helps.