How did the Sheikh conclude that it is not from the Sunnah to shave a girl's head? Is there harm to girls in their hair as well? Is there a difference of opinion on this matter?

The jurists have recommended shaving the head hair of a male newborn, but they differed concerning shaving the hair of a female. The Maliki and Shafi'i schools of thought considered it recommended, while the Hanbali school considered it not recommended due to the lack of an authentic text regarding it, and because the default rule is the prohibition of shaving a woman's hair, as it involves disfigurement (muthlah) and constitutes an alteration of Allah's creation. As for "removing the harm" mentioned in the hadith, it has been interpreted as either shaving the head or removing dirt and blood from the head.